docs: ✏️ cleanup and organize docs

docs/features/symbol-editor/0001-symbol-editor-port.md

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+# Symbol Editor WASM port — design notes
+
+## Goal
+
+Bring up KiCad's Symbol Editor (`FRAME_SCH_SYMBOL_EDITOR`, the `.kicad_sym`
+library editor) in the browser, to the same "boots, canvas visible, click
+around" level as the other ported apps. Scope is launch-only — library
+load/save and the symbol viewer/chooser sub-frames are out of scope for now.
+
+## Key insight
+
+Unlike pcbnew / pl_editor, the symbol editor is **not a separate program**. It is
+served by the **eeschema kiface**: its sources already compile into
+`eeschema_kiface_objects` (`EESCHEMA_LIBEDIT_SRCS` + the `symbol_editor_*` tools in
+`kicad/eeschema/CMakeLists.txt`). KiCad's universal launcher `common/single_top.cpp`
+opens whichever frame the compile-time `TOP_FRAME` macro names.
+
+So the port is just **a second launcher executable (`symbol_editor`) that links the
+same eeschema kiface but compiles `single_top.cpp` with
+`TOP_FRAME=FRAME_SCH_SYMBOL_EDITOR`** — no new sources, no new kiface, no extracting
+symbol-editor code. The eeschema kiface (deps, navlib, stubs, libraries) is reused
+verbatim.
+
+## Changes
+
+### kicad submodule (2 files)
+
+- **`kicad/eeschema/CMakeLists.txt`** — a WASM-only (`if( EMSCRIPTEN )`) block adds the
+  `symbol_editor` executable. Because `single_top.cpp`'s `COMPILE_DEFINITIONS` are
+  directory-scoped (already pinned to `TOP_FRAME=FRAME_SCH` for the `eeschema` exe),
+  we `configure_file`-copy it to a private TU (`symbol_editor_single_top.cpp`) and set
+  that copy's `TOP_FRAME=FRAME_SCH_SYMBOL_EDITOR;PGM_DATA_FILE_EXT="kicad_sym"`. The exe
+  links `EESCHEMA_KIFACE_LIBRARIES` directly with `LINKER:--allow-multiple-definition`,
+  mirroring the eeschema/pcbnew static-link pattern.
+- **`kicad/eeschema/eeschema.cpp`** — `IFACE::CreateKiWindow`'s `FRAME_SCH_SYMBOL_EDITOR`
+  case was stubbed to `return nullptr` on `__EMSCRIPTEN__` during the eeschema MVP
+  (see `../schematic/0001-eeschema-iface-stubs.md`). That stub is now removed so
+  the frame is constructed in WASM like the native build. This was THE blocker: with the
+  stub, `Kiway.Player(FRAME_SCH_SYMBOL_EDITOR)` returned null, `single_top`'s `OnInit`
+  bailed, and the app sat idle with a blank canvas (no abort, no error).
+
+  The symbol viewer (`FRAME_SCH_VIEWER`) and chooser (`FRAME_SYMBOL_CHOOSER`) remain
+  stubbed — out of scope, and the chooser needs bundled libraries we don't ship.
+
+### Root repo
+
+- **`scripts/kicad/build-symbol_editor.sh`** — thin wrapper around
+  `build-kicad-target.sh symbol_editor`.
+- **`scripts/kicad/build-kicad-target.sh`** — adds `symbol_editor` to the `case`. CMake
+  target is `symbol_editor` but its build subdir is `eeschema` (it's part of that
+  kiface), so a `KICAD_SUBDIR` variable now distinguishes target name from subdir for
+  the output-path log and embind include.
+- **`docker/build.sh`** — adds `symbol_editor` to valid apps, the `all` loop, and
+  `kicad_subdir_for` (`symbol_editor → eeschema`); artifacts land at
+  `build-wasm/kicad-symbol_editor/eeschema/symbol_editor.{js,wasm}`.
+- **`tests/apps/kicad/symbol_editor.html`** — browser shell (copy of eeschema.html with
+  title + `thisProgram=/usr/bin/symbol_editor` + `symbol_editor.js`).
+- **`tests/scripts/setup-kicad-wasm.sh`** — `copy_app symbol_editor` + subdir map entry.
+- **`tests/kicad/symbol_editor.spec.ts`** + **`tests/package.json`** — launch-scope smoke
+  test (canvas visible, registry populated, toolbars present, no WASM abort), mirroring
+  eeschema's wizard-aware flow.
+
+### wxwidgets submodule
+
+No changes needed — the file-dialog and double-click fixes landed with the pl_editor port.
+
+## Build & verify
+
+```
+./docker/build.sh symbol_editor
+cd tests && npm run setup:kicad && npm run test:symbol_editor
+# or serve tests/apps/kicad and open symbol_editor.html
+```
+
+Expect: the symbol editor window opens — menu bar, top + left + right toolbars
+(incl. pin/rect/circle/line drawing tools), the symbol library tree pane with the
+filter box, the gridded canvas with the symbol-origin crosshair, and a status bar.
+
+## Known limitations
+
+- No bundled symbol libraries, so the library tree is empty (`SyncLibraries` reports
+  `libCount=0`). Opening/creating/saving `.kicad_sym` files is untested (out of scope).
+- Symbol viewer and symbol chooser frames are still stubbed out for WASM.
+- No persistent storage (MEMFS only).
+</content>