Remove the Windows 7 (7.css) skin

The win7 skin is dropped. Everything else the branch built stays: Linux
support and the HTML context menus, the workspace-tab menu, the continuous
interface scale (rem everywhere, stepper, Ctrl/Cmd +/-/0) and the core/
service layer. The modern tree already carried all of them, and nothing
outside skins/7like/ imported the win7 tree except main.ts and styles.css.

Removed: the skins/7like/ tree (5.1k lines, fonts), the 7.css dependency,
the skin setting and its options row + strings in all 7 locales, the
frameless-window plumbing (window-control RPCs, windowState push,
trackMaximizeState, the synthesized resize grip and its postinstall
watchdog), the session-skin pinning in buildPreload/chromeOptions, the
skin/skinfix cascade layers, and the win7-only probes and screenshot
harness (the harness cannot render the modern tree: plain Firefox has no
RPC bridge). chromeOptions() stays as the one shared frame decision.

Fixed on the way out:
- index.html's per-theme pre-paint background is restored. The branch had
  replaced it with a win7-only transparent rule, so modern dark windows had
  silently lost one of the three flash guards.
- editor-windows.ts wrote its window-key separator as a literal NUL byte,
  which made git and grep treat the file as binary; it is `\0` now (same
  string at runtime).

No settings migration: a stale "skin" key is carried harmlessly by the
store's spread-merge and dropped on the next save.

UI bundle: 616.7 kB -> 405.4 kB, back under the 500 kB budget.

Docs: architecture, gotchas and platform-notes lose the win7 material but
keep what stays true (construction-time preloads/frames, drag regions
ignoring preventDefault, electrobun's missing resize/maximize primitives);
flash-prevention, dev-URL and Bun-panic notes move back under Electrobun;
stale context-menu/tab-bar links fixed; README documents the scale keys.

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

src/shared/rpc.ts

@@ -128,7 +128,7 @@ export type AppRPC = {
 			// local shell integration
 			/**
 			 * Shell actions the context menu triggers on a LOCAL path. The menu
-			 * itself is HTML (ui/src/app/context-menu.ts) — electrobun's native
+			 * itself is HTML (ui/src/app/core/context-menu.service.ts) — electrobun's native
 			 * context menu is a no-op on Linux — but these three still need the
 			 * bun side's Utils.
 			 */
@@ -154,35 +154,6 @@ 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 }>;
-			};
-			/**
-			 * STOPGAP — the two halves of the synthesized resize. A frameless GTK
-			 * window has no resize borders and electrobun exposes no native resize
-			 * gesture, so the webview drags its own handles and moves the frame
-			 * itself. Delete both with the rest of the hack; see the removal
-			 * checklist in ui/src/app/skins/7like/window-resize/window-resize.ts.
-			 */
-			windowGetFrame: {
-				params: Record<string, never>;
-				response: Result<{ x: number; y: number; width: number; height: number }>;
-			};
-			windowSetFrame: {
-				params: { x: number; y: number; width: number; height: number };
-				response: Result;
-			};
 			// auto-updater (electrobun Updater)
 			/** Main window: re-run the update check on demand (menu item). */
 			checkForUpdate: {
@@ -213,13 +184,6 @@ 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>;
 			/**