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>

docs/gotchas.md

@@ -28,6 +28,21 @@ touching the adjacent code.
 - Tailwind v4 canonical class names: `wrap-break-word` not `break-words`,
   `accent-primary` not `accent-[var(--primary)]`, `z-60` not `z-[60]`.
   Every color used in a template must resolve through `@theme inline`.
+- **The win7 skin layer outranks Tailwind utilities.** 7.css is imported
+  `layer(skin)`, ordered above `utilities`, so any utility you add to a
+  `button`/`input`/`select`/`textarea`/`table` is silently dead under that
+  skin. If it matters, neutralize in the `@layer skin` block at the bottom of
+  styles.css — and note `revert-layer` only reaches `utilities` from **inside
+  `skin`**; used from `skinfix` it falls back onto 7.css and is a no-op. This
+  bit once already.
+- `@import … layer(name)` works through `@tailwindcss/postcss` (it wraps the
+  imported AST), but the **deep path is mandatory**: 7.css ships no `exports`
+  map and Tailwind's resolver reads only `style`/`mainFields`, so a bare
+  `@import "7.css"` resolves to nothing. Use `7.css/dist/7.scoped.css`.
+- Stylesheet `url()` must resolve at BUILD time: assets referenced from
+  `styles.css` live under `ui/src/` (esbuild emits them hashed into `media/`
+  and rewrites the url), NOT `ui/public/` — a public path fails the build with
+  "Could not resolve".
 
 ## Electrobun
 
@@ -56,6 +71,13 @@ touching the adjacent code.
   attributes before first paint (`buildPreload`), (3) `ui/src/index.html`
   carries an inline `<style>` with the html background per theme — its oklch
   values MUST stay in sync with the `--background` tokens in styles.css.
+  The win7 skin adds a **fourth value to keep in sync**: `buildPreload` also
+  bakes the `.win7` class, and index.html carries a matching `html.win7` arm
+  for all four theme states. Miss it and every win7 window flashes white.
+- **`titleBarStyle` is construction-time only.** Switching skin cannot
+  re-frame a live window; `chromeOptions` is read once per `new
+  BrowserWindow`. The options row tells the user to reopen. Don't "fix" this
+  by recreating the main window — that would drop every session and tab.
 - Dev vs prod URL: `getMainViewUrl()` resolves the ng-serve dev server only
   when `DEV_SERVER_URL` is set AND the updater channel is `dev` AND the
   server answers a HEAD request; secondary windows must reuse the resolved