Add a toggleable Windows 7 (7.css) skin behind a new skin setting

Evaluation branch: a full Aero skin, including frameless windows with our own
title bar, switchable against the existing modern look.

The app already had a four-axis runtime skinning mechanism and zero component
stylesheets, so the skin is one new setting plus one stylesheet section rather
than a parallel UI. The key move is cascade order: 7.css is imported into a
`skin` layer ABOVE Tailwind's `utilities`, so its bare element rules outrank
the ~1900 inline utility classes already in the templates. Template changes are
limited to additive, skin-inert hooks (ARIA roles, `has-scrollbar`,
`w7-toolbar`, `w7-btn`).

- styles.css: explicit layer order, `7.css/dist/7.scoped.css` via `layer(skin)`,
  a token bridge re-pointing the existing semantic tokens at Win7 values (no new
  tokens, so `@theme inline` is untouched), a hand-authored dark Win7 palette,
  and neutralizers that `revert-layer` 7.css's dialog-button metrics back to the
  utility layer. Neutralizers must live inside `skin`, not `skinfix` —
  `revert-layer` only reaches `utilities` from one layer up.
- Frameless chrome: `chromeOptions(skin)` is now the single place either skin's
  frame is decided. `titleBarStyle: "hidden"` on every platform, which is also
  the only way to drop the macOS traffic lights. New `title-bar` component
  mounted by all three window roots.
- Window controls over RPC (minimize/toggle-maximize/close/is-maximized), served
  per window kind so the X reuses each one's existing close path — editors still
  get their dirty prompt. electrobun has no maximize event, so the state is
  derived from `resize`; double-click-to-maximize is implemented here too.
- Font: Noto Sans vendored (OFL-1.1) under ui/src/fonts, since Segoe UI is
  absent off Windows and not redistributable.

Verified: backend `tsc --noEmit` clean, `bun run build:ui` clean (486 kB initial,
under the 500 kB budget), app launches with the skin active and no console
errors. The rendered result has not been eyeballed — screen capture and
accessibility are both denied to the shell on this machine.

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

bun.lock

@@ -21,6 +21,7 @@
       "name": "ui",
       "version": "0.0.0",
       "dependencies": {
+        "7.css": "^0.21.1",
         "@angular/common": "^22.0.0",
         "@angular/compiler": "^22.0.0",
         "@angular/core": "^22.0.0",
@@ -45,6 +46,8 @@
     "@parcel/watcher",
   ],
   "packages": {
+    "7.css": ["7.css@0.21.1", "", {}, "sha512-Q+/aFUpGemoR/Zltj4a7yvHonyxfb+9cgiwBL+j/Lm+H28EOoLzWoJki7MdGPV+3mLCvKSCVqr3M2x2uNYyeWw=="],
+
     "@algolia/abtesting": ["@algolia/abtesting@1.18.0", "", { "dependencies": { "@algolia/client-common": "5.52.0", "@algolia/requester-browser-xhr": "5.52.0", "@algolia/requester-fetch": "5.52.0", "@algolia/requester-node-http": "5.52.0" } }, "sha512-8siuLG+FIns1AjZ/g2SDVwHz9S+ObacDQISEJvS8XsNei1zl3FXqfqQrBpmrG7ACWCyesXHbicMJtvRbg00FEw=="],
 
     "@algolia/client-abtesting": ["@algolia/client-abtesting@5.52.0", "", { "dependencies": { "@algolia/client-common": "5.52.0", "@algolia/requester-browser-xhr": "5.52.0", "@algolia/requester-fetch": "5.52.0", "@algolia/requester-node-http": "5.52.0" } }, "sha512-wtwPgyPmO7b7sQPVgoK29c1VpfS08DnnJCmxX/oU1pV2DlMRJCzQcLN7JSloYpodyKHwM8+9wOzlAM0co3TDmA=="],