feat(text): TEXTFILL — fill or hollow TrueType glyphs (#260)

TEXTFILL 1 (default) fills TrueType text; TEXTFILL 0 draws it hollow
(outline only). Settable directly or via SETVAR, 0/1 or ON/OFF. SHX/LFF
stroke fonts are unaffected.

Reuses the existing stroke-SDF path: bake_glyph treats a TTF glyph as a
stroke (outline) field instead of a signed fill field when TEXTFILL is
off. Toggling resets the glyph atlas and re-tessellates text so quads
pick up the re-baked tiles. Persisted in user settings.

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

src/app/commands/mod.rs

@@ -328,6 +328,7 @@ inventory::submit!(crate::command::CommandRegistration {
         "TCASE",
         "TEXTMASK",
         "TEXTFIT",
+        "TEXTFILL",
         "TCOUNT",
         "ARCTEXT",
         // Jogged radius dimension.