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>

ui/src/app/title-bar/title-bar.ts

@@ -0,0 +1,72 @@
+import { Component, inject, input, output, signal } from '@angular/core';
+import { IS_WIN7_CHROME } from '../platform';
+import { RpcService } from '../rpc.service';
+
+/**
+ * The win7 skin's Aero title bar. Rendered by all three window kinds, and only
+ * when `IS_WIN7_CHROME` — under that skin the native frame is gone
+ * (titleBarStyle 'hidden'), so this row IS the window's chrome.
+ *
+ * The markup is 7.css's contract, not ours: `.title-bar` > `.title-bar-text` +
+ * `.title-bar-controls` > buttons keyed by `aria-label` (Minimize / Maximize /
+ * Restore / Close each get their own glyph). Nothing here is styled with
+ * Tailwind on purpose — the whole row comes from @layer skin.
+ *
+ * Dragging rides on electrobun's preload drag-region classes. Two things
+ * electrobun does NOT provide and this component implements:
+ *   - double-click to maximize (it only wires mousedown/mouseup)
+ *   - the maximize/restore glyph state, which has no event; bun derives it
+ *     from the native resize and pushes `windowState` (see trackMaximizeState).
+ */
+@Component({
+  selector: 'app-title-bar',
+  template: `
+    @if (enabled) {
+      <div class="title-bar electrobun-webkit-app-region-drag" (dblclick)="toggle()">
+        <div class="title-bar-text">{{ title() }}</div>
+        <div class="title-bar-controls electrobun-webkit-app-region-no-drag">
+          @if (resizable()) {
+            <button aria-label="Minimize" (click)="minimize()"></button>
+            <button
+              [attr.aria-label]="maximized() ? 'Restore' : 'Maximize'"
+              (click)="toggle()"
+            ></button>
+          }
+          <button aria-label="Close" (click)="closeRequested.emit()"></button>
+        </div>
+      </div>
+    }
+  `,
+})
+export class TitleBar {
+  readonly title = input('');
+  /** The manager window is a fixed-size modal — it gets Close only. */
+  readonly resizable = input(true);
+  /** Hosts decide what closing means (quit / dirty prompt / managerClose). */
+  readonly closeRequested = output<void>();
+
+  protected readonly enabled = IS_WIN7_CHROME;
+  protected readonly maximized = signal(false);
+
+  private readonly rpc = inject(RpcService);
+
+  constructor() {
+    if (!this.enabled || !this.rpc.available) return;
+    // No maximize event exists, so seed from a one-shot read and then follow
+    // the resize-derived push (which also covers Aero Snap and Win+Up).
+    void this.rpc.request.windowIsMaximized({}).then((res) => {
+      if (res.ok) this.maximized.set(res.maximized);
+    });
+    this.rpc.onWindowState((maximized) => this.maximized.set(maximized));
+  }
+
+  protected minimize(): void {
+    void this.rpc.request.windowMinimize({});
+  }
+
+  protected toggle(): void {
+    void this.rpc.request.windowToggleMaximize({}).then((res) => {
+      if (res.ok) this.maximized.set(res.maximized);
+    });
+  }
+}