feat(icons): file icons and tab glyphs in color, from the host's own artwork

Issue #611 asked for file-type icons like the official explorer's, and #429
built a colored theme for them. DSH 0.1.5-rc.2 makes most of that work
unnecessary: `@deepseek-ai/dsh-client-ui-primitives` now exports
`FileTypeIcon` / `CodeFileIcon` with the host's own 48-type full-color code
artwork plus category-colored sheet glyphs (and its classifier behind them).
So the plugin renders the host's icons instead of shipping a color table, and
color becomes the only behaviour rather than an opt-in theme.

File icons (src/client/file-icons.tsx)
- `builtinFileIcon(path, size)` → `<FileTypeIcon path size />`; folders use the
  host's folder category. The plugin's own per-extension VSCodicon map is gone.
- The public `registerFileIcon` API from #531 is unchanged and still outranks
  the built-ins, so an external plugin can take over any row. One semantic
  consequence, now documented and tested: because the host classifier covers
  every path, a registered catch-all (`exts: []`) claims rows it used to lose
  to the built-in map. An unregistered catch-all (the old icon theme's shape)
  is unaffected.
- Nothing is lazy any more: the artwork lives in a platform module the client
  already holds, so `lib/client-file-icons.js` and its 563-entry dataset (255
  kB) are deleted outright — the core bundle grew by 10 kB (0.85 → 0.86 MB).
- `src/client/file-icon-theme.ts`, the `fileIconTheme` pref (prefs-shared /
  config / client prefs), the settings-page select row and the six
  `settingsFileIconTheme*` keys in all 20 dictionaries are removed with it.

Tab glyphs (src/client/builtins/tab-icons.tsx)
- Every built-in tab type now declares a colored glyph: files (the host's
  folder artwork), changes/diff (commit), tasks (checklist), side chat
  (discussion), terminal (shell), browser (globe).
- The color comes from a `--dsw-alias-*` token through a wrapper class, never
  from a literal — the skin contract (§12) holds and `tests/theme.spec.ts`
  enforces both halves (no literals in the module, every color declaration in
  the stylesheet resolves to a token).

Native right Sidebar chips (src/client/native/tab-adapter.tsx)
- The host's tab definition has no icon field, but the
  `sidebar.right.pane.tab.title` slot IS the chip's content, so the plugin
  draws the glyph itself: an editor tab with a path shows that file's icon,
  every other tab shows its descriptor's icon — the same `descriptor.icon` the
  workbench strip and the guide capsules already render, so the three cannot
  drift. The glyph is `aria-hidden`, which keeps the chip's accessible name
  exactly the title the mount lane matches on.

Gates: typecheck / lint / check:consumer-types green; pnpm test 127 files /
1342 passed / 9 skipped (3 new chip cases, 1 rewritten built-in case).

tests/builtins.spec.ts

@@ -136,7 +136,7 @@ describe('built-in tab registrations', () => {
   it('the editor tab declares its merged-mode (embedded file tree) setting', () => {
     const { service } = setup()
     const toggles = service.getTab('editor')?.settings?.toggles ?? []
-    expect(toggles.map(t => t.key)).toEqual(['editorExplorer', 'workspaceFence', 'fileIconTheme'])
+    expect(toggles.map(t => t.key)).toEqual(['editorExplorer', 'workspaceFence'])
     expect(toggles[0]?.title).toBeDefined()
     expect(toggles[0]?.desc).toBeDefined()
     // The merged mode is an iconed select (merged vs separate), not a switch.