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/shared/rpc.ts

@@ -157,6 +157,20 @@ export type AppRPC = {
 			managerConnect: { params: { id: string }; response: Result };
 			managerOpenStack: { params: { id: string }; response: Result };
 			managerClose: { params: Record<string, never>; response: Result };
+			// custom window chrome (win7 skin — the window is frameless, so the
+			// webview's title bar owns the controls). Served by every window kind.
+			windowMinimize: { params: Record<string, never>; response: Result };
+			/** Maximize/restore in one call; responds with the resulting state. */
+			windowToggleMaximize: {
+				params: Record<string, never>;
+				response: Result<{ maximized: boolean }>;
+			};
+			windowClose: { params: Record<string, never>; response: Result };
+			/** First paint: the title bar needs the state before any resize fires. */
+			windowIsMaximized: {
+				params: Record<string, never>;
+				response: Result<{ maximized: boolean }>;
+			};
 			// auto-updater (electrobun Updater)
 			/** Main window: re-run the update check on demand (menu item). */
 			checkForUpdate: {
@@ -187,6 +201,13 @@ export type AppRPC = {
 			editorCloseRequest: Record<string, never>;
 			/** bun → main: the modal connection manager opened/closed. */
 			managerState: { open: boolean };
+			/**
+			 * bun → any window: maximize state changed, so the custom title bar can
+			 * swap its maximize/restore glyph. electrobun has no maximize event —
+			 * this is derived from the window's `resize` event (see windows.ts
+			 * trackMaximizeState), which also covers OS-initiated Aero Snap.
+			 */
+			windowState: { maximized: boolean };
 			/** bun → main: the manager window changed the connection store. */
 			connectionsChanged: Record<string, never>;
 			/**