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>

src/bun/index.ts

@@ -16,7 +16,7 @@ import { migrateLegacyDataDir } from "./store/paths";
 import { SettingsStore } from "./store/settings";
 import { AppTray } from "./tray";
 import { TransferEngine } from "./transfers/engine";
-import { buildPreload, showWhenReady } from "./windows";
+import { buildPreload, chromeOptions, showWhenReady, trackMaximizeState } from "./windows";
 
 const PROD_URL = "views://app/index.html";
 
@@ -56,7 +56,20 @@ const events = {
 	openConnectionManager: () => {},
 	showAbout: () => {},
 };
-const rpc = createAppRPC({ registry, engine, store, settings, edits, contextMenu, watcher, events });
+// Late-bound for the same reason events is: `win` below takes this rpc in its
+// constructor, so it cannot exist yet. Only the win7 title bar reads it.
+let mainWin: BrowserWindow | undefined;
+const rpc = createAppRPC({
+	registry,
+	engine,
+	store,
+	settings,
+	edits,
+	contextMenu,
+	watcher,
+	mainWindow: () => mainWin,
+	events,
+});
 // late-bound like events: a watched local dir changed -> tell the main webview
 watcher.onChange = (dir) => rpc.send.pathRefresh({ sessionId: "local", dir });
 const url = await getMainViewUrl();
@@ -67,8 +80,6 @@ const url = await getMainViewUrl();
 let currentSettings = await settings.load();
 setBackendLocale(currentSettings.locale); // native menus/errors follow the UI language
 
-const isMac = process.platform === "darwin";
-
 const win = new BrowserWindow({
 	title: BRANDING.appName,
 	url,
@@ -78,12 +89,8 @@ const win = new BrowserWindow({
 		x: 120,
 		y: 120,
 	},
-	// macOS: fuse the tab bar with the titlebar — traffic lights overlay the
-	// UI's h-10 tab row (offset centers them vertically). Other platforms keep
-	// the native titlebar and the tab bar stays a separate row.
-	...(isMac
-		? { titleBarStyle: "hiddenInset" as const, trafficLightOffset: { x: 12, y: 13 } }
-		: {}),
+	// Frame decision (per skin) lives in chromeOptions — see windows.ts.
+	...chromeOptions(currentSettings.skin),
 	// lets the UI pick the fused layout + theme before first paint
 	preload: buildPreload("main", currentSettings),
 	rpc,
@@ -91,6 +98,8 @@ const win = new BrowserWindow({
 	hidden: true,
 });
 showWhenReady(win);
+mainWin = win;
+trackMaximizeState(win, (maximized) => rpc.send.windowState({ maximized }));
 
 const editors = new EditorWindows({
 	registry,