feat(web): lazy per-script font loading for international CAD text

The web build has no system-font access, so CAD text in non-Latin scripts
(Cyrillic, Greek, CJK, …) rendered as nothing — build_fallback was a hard
None on wasm (#141). Instead, ship per-script Noto subsets under web/fonts
(one alphabet per file, SIL OFL 1.1) and fetch them lazily over HTTP the
first time a drawing uses that script, then outline glyphs with ttf-parser.

- web_font: Script enum + script_of (char → script font), a per-script
  store with lazy fetch, and a pending queue drained by the app loop.
- CJK is split by language (chinese/japanese/korean). Han ideographs share
  code points but differ by language, so the shared block is routed by the
  document's $DWGCODEPAGE (932→JP, 949→KR, GB/936→CN); kana is always
  Japanese, Hangul always Korean. Re-tessellates when the language changes.
- build_fallback (wasm) outlines from the fetched subset; clear_fallback_cache
  lets glyphs that missed while a font was in flight reappear on load.
- PollWebFonts subscription (web only) + WebFontLoaded message drive fetches.
- Trunk copy-dir serves web/fonts; nothing is bundled into the native binary
  (desktop keeps using system fonts).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/fonts/OFL.txt

@@ -0,0 +1,102 @@
+The fonts in this directory are subsets of Google's Noto fonts, generated by
+generate.sh. They are redistributed under the SIL Open Font License v1.1.
+
+Copyright 2022 The Noto Project Authors (https://github.com/notofonts/latin-greek-cyrillic)
+Copyright 2022 The Noto Project Authors (https://github.com/notofonts/arabic)
+Copyright 2022 The Noto Project Authors (https://github.com/notofonts/hebrew)
+Copyright 2022 The Noto Project Authors (https://github.com/notofonts/thai)
+Copyright 2022 The Noto Project Authors (https://github.com/notofonts/devanagari)
+Copyright 2014-2021 Adobe (http://www.adobe.com/), with Reserved Font Name 'Source'. (Noto Sans CJK)
+Noto is a trademark of Google LLC. Noto has no Reserved Font Name.
+
+This Font Software is licensed under the SIL Open Font License, Version 1.1.
+This license is copied below, and is also available with a FAQ at:
+https://openfontlicense.org
+
+
+-----------------------------------------------------------
+SIL OPEN FONT LICENSE Version 1.1 - 26 February 2007
+-----------------------------------------------------------
+
+PREAMBLE
+The goals of the Open Font License (OFL) are to stimulate worldwide
+development of collaborative font projects, to support the font creation
+efforts of academic and linguistic communities, and to provide a free and
+open framework in which fonts may be shared and improved in partnership
+with others.
+
+The OFL allows the licensed fonts to be used, studied, modified and
+redistributed freely as long as they are not sold by themselves. The
+fonts, including any derivative works, can be bundled, embedded,
+redistributed and/or sold with any software provided that any reserved
+names are not used by derivative works. The fonts and derivatives,
+however, cannot be released under any other type of license. The
+requirement for fonts to remain under this license does not apply
+to any document created using the fonts or their derivatives.
+
+DEFINITIONS
+"Font Software" refers to the set of files released by the Copyright
+Holder(s) under this license and clearly marked as such. This may
+include source files, build scripts and documentation.
+
+"Reserved Font Name" refers to any names specified as such after the
+copyright statement(s).
+
+"Original Version" refers to the collection of Font Software components as
+distributed by the Copyright Holder(s).
+
+"Modified Version" refers to any derivative made by adding to, deleting,
+or substituting -- in part or in whole -- any of the components of the
+Original Version, by changing formats or by porting the Font Software to a
+new environment.
+
+"Author" refers to any designer, engineer, programmer, technical
+writer or other person who contributed to the Font Software.
+
+PERMISSION & CONDITIONS
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of the Font Software, to use, study, copy, merge, embed, modify,
+redistribute, and sell modified and unmodified copies of the Font
+Software, subject to the following conditions:
+
+1) Neither the Font Software nor any of its individual components,
+in Original or Modified Versions, may be sold by itself.
+
+2) Original or Modified Versions of the Font Software may be bundled,
+redistributed and/or sold with any software, provided that each copy
+contains the above copyright notice and this license. These can be
+included either as stand-alone text files, human-readable headers or
+in the appropriate machine-readable metadata fields within text or
+binary files as long as those fields can be easily viewed by the user.
+
+3) No Modified Version of the Font Software may use the Reserved Font
+Name(s) unless explicit written permission is granted by the corresponding
+Copyright Holder. This restriction only applies to the primary font name as
+presented to the users.
+
+4) The name(s) of the Copyright Holder(s) or the Author(s) of the Font
+Software shall not be used to promote, endorse or advertise any
+Modified Version, except to acknowledge the contribution(s) of the
+Copyright Holder(s) and the Author(s) or with their explicit written
+permission.
+
+5) The Font Software, modified or unmodified, in part or in whole,
+must be distributed entirely under this license, and must not be
+distributed under any other license. The requirement for fonts to
+remain under this license does not apply to any document created
+using the Font Software.
+
+TERMINATION
+This license becomes null and void if any of the above conditions are
+not met.
+
+DISCLAIMER
+THE FONT SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT
+OF COPYRIGHT, PATENT, TRADEMARK, OR OTHER RIGHT. IN NO EVENT SHALL THE
+COPYRIGHT HOLDER BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
+INCLUDING ANY GENERAL, SPECIAL, INDIRECT, INCIDENTAL, OR CONSEQUENTIAL
+DAMAGES, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+FROM, OUT OF THE USE OR INABILITY TO USE THE FONT SOFTWARE OR FROM
+OTHER DEALINGS IN THE FONT SOFTWARE.

web/fonts/generate.sh

@@ -0,0 +1,46 @@
+#!/usr/bin/env bash
+# Regenerate the per-script Noto subsets served to the web build.
+# Each script lives in its own TTF so a browser only fetches the alphabets a
+# drawing actually uses. Source: Noto fonts (SIL OFL 1.1 — see OFL.txt).
+#
+# Requires: pip install --break-system-packages fonttools brotli
+set -euo pipefail
+RAW="https://github.com/notofonts/notofonts.github.io/raw/main/fonts"
+sub() { python3 -m fontTools.subset "$1" --unicodes="$2" --output-file="$3" \
+        --no-hinting --desubroutinize --layout-features='*' --notdef-outline \
+        --name-IDs='*' --recalc-bounds 2>/dev/null; }
+dl() { curl -sL -o "$1" "$2"; }
+
+# Latin / Cyrillic / Greek share one Noto source.
+dl /tmp/NotoSans.ttf "$RAW/NotoSans/hinted/ttf/NotoSans-Regular.ttf"
+sub /tmp/NotoSans.ttf "U+0000-024F,U+1E00-1EFF,U+2000-206F,U+20A0-20BF,U+2122,U+2190-21FF,U+2200-22FF" latin.ttf
+sub /tmp/NotoSans.ttf "U+0400-04FF,U+0500-052F,U+2DE0-2DFF,U+A640-A69F" cyrillic.ttf
+sub /tmp/NotoSans.ttf "U+0370-03FF,U+1F00-1FFF" greek.ttf
+
+# One source per remaining script.
+dl /tmp/NotoArabic.ttf "$RAW/NotoSansArabic/hinted/ttf/NotoSansArabic-Regular.ttf"
+sub /tmp/NotoArabic.ttf "U+0600-06FF,U+0750-077F,U+08A0-08FF,U+FB50-FDFF,U+FE70-FEFF" arabic.ttf
+
+dl /tmp/NotoHebrew.ttf "$RAW/NotoSansHebrew/hinted/ttf/NotoSansHebrew-Regular.ttf"
+sub /tmp/NotoHebrew.ttf "U+0590-05FF,U+FB1D-FB4F" hebrew.ttf
+
+dl /tmp/NotoThai.ttf "$RAW/NotoSansThai/hinted/ttf/NotoSansThai-Regular.ttf"
+sub /tmp/NotoThai.ttf "U+0E00-0E7F" thai.ttf
+
+dl /tmp/NotoDeva.ttf "$RAW/NotoSansDevanagari/hinted/ttf/NotoSansDevanagari-Regular.ttf"
+sub /tmp/NotoDeva.ttf "U+0900-097F,U+A8E0-A8FF" devanagari.ttf
+
+# CJK comes from the noto-cjk repo (CFF/OTF; ttf-parser reads CFF outlines) and
+# is split by language: Chinese, Japanese and Korean each get their own file.
+# Han ideographs share code points but differ in glyph shape, so each language
+# ships its own. These are the heavy ones — lazy-loaded per language only when a
+# drawing in that language is opened.
+CJK="https://github.com/notofonts/noto-cjk/raw/main/Sans/OTF"
+dl /tmp/NotoSC.otf "$CJK/SimplifiedChinese/NotoSansCJKsc-Regular.otf"
+sub /tmp/NotoSC.otf "U+3000-303F,U+4E00-9FFF,U+FF00-FFEF" chinese.ttf
+
+dl /tmp/NotoJP.otf "$CJK/Japanese/NotoSansCJKjp-Regular.otf"
+sub /tmp/NotoJP.otf "U+3000-303F,U+3040-30FF,U+31F0-31FF,U+4E00-9FFF,U+FF00-FFEF" japanese.ttf
+
+dl /tmp/NotoKR.otf "$CJK/Korean/NotoSansCJKkr-Regular.otf"
+sub /tmp/NotoKR.otf "U+1100-11FF,U+3130-318F,U+AC00-D7A3" korean.ttf