Switch the UI icons from mynaui to TDesign

Swap @ng-icons/mynaui for @ng-icons/tdesign-icons (34.0.0, the release
matching @ng-icons/core), drawn at TDesign's native stroke. Each former
mynaui name maps to one TDesign name everywhere it was used; the unused
ArrowLeftRight is dropped. The options button's ellipsis goes from 1.5rem
to 0.8rem: TDesign's dots span 18 of 24 units against mynaui's 8, so this
keeps today's footprint.

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

docs/architecture.md

@@ -265,6 +265,10 @@ component; tokens → `ui/src/styles.css`.
   walker check the flag themselves.
 - `file-icons.ts` — extension → category map driving glyphs, colors
   (fixed `--icon-*` tokens, never accent-tinted) and the Kind column.
+- `icons.ts` — the one icon registry (TDesign, `@ng-icons/tdesign-icons`), passed to
+  `provideIcons` in `app.config.ts`. Icon names are plain strings in templates and
+  the build never checks them: an unregistered name renders nothing (console error
+  only), so every name used anywhere must be listed here.
 - `platform.ts` — preload-global readers (`PLATFORM`, `APP_MODE`,
   `EDITOR_CONTEXT`, `IS_MAC`/`IS_MAC_CHROME`, `IS_WINDOWS`, `IS_LINUX`,
   `MOD_LABEL`/`ALT_LABEL`) + `blockNativeContextMenu` (kills WebKit's