fix(ui): Match PyCharm project view, matched tags and text weight

- Project widget initials follow IDEA's AvatarUtils.initials ("idea" → "I").
- "Show directories with changed descendants" is off by default, as in IDEA.
- FileEntry gains `excluded`: only excluded folders get the excluded icon and
  dimming; git-ignored ones keep the plain icon and the ignored colour.
- `.github` folders get IDEA's GitHub folder icon.
- Matched tag names are never bold and use their own background
  (MATCHED_TAG_NAME); matched braces are bold in dark schemes only.
- Revert Greyscale antialiasing to `antialiased` for UI and editor; `auto`
  rendered text heavier than PyCharm.

Claude-Session: https://claude.ai/code/session_01SaPPsVPuk6ZTNsoUCNCbMv

src/features/project-tree/contextMenu.test.ts

@@ -19,6 +19,7 @@ const node = (path: string, dir = false, root = false): ProjectNode => ({
   root,
   entry: null,
   ignored: false,
+  excluded: false,
   symlink: false,
 });