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/bun/rpc-handlers.ts

@@ -1,4 +1,4 @@
-import { BrowserView, type BrowserWindow, Updater, Utils } from "electrobun/bun";
+import { BrowserView, Updater, Utils } from "electrobun/bun";
 import type { AppRPC, EditorOpenContext } from "../shared/rpc";
 import { effectiveConcurrency, type AppSettings, type Result } from "../shared/types";
 import { readFileText, writeFileText, type EditManager } from "./edits";
@@ -24,12 +24,6 @@ export interface AppDeps {
 	settings: SettingsStore;
 	edits: EditManager;
 	watcher: LocalDirWatcher;
-	/**
-	 * The main BrowserWindow, for the win7 skin's custom title-bar controls.
-	 * Lazy for the same reason events is late-bound: the window takes this rpc
-	 * instance in its constructor, so it does not exist yet at createAppRPC time.
-	 */
-	mainWindow: () => BrowserWindow | undefined;
 	/** Assigned after the rpc object exists (it needs rpc.send). */
 	events: {
 		sessionClosed: (info: { sessionId: string; reason: string }) => void;
@@ -49,78 +43,6 @@ async function wrap<T extends object>(fn: () => Promise<T> | T): Promise<Result<
 	}
 }
 
-/**
- * Window-control requests for the win7 skin's custom title bar. Shared by all
- * three window kinds; each passes a getter for ITS OWN window.
- *
- * The getter is lazy because the main window's rpc instance is constructed
- * before the BrowserWindow exists (the window takes the rpc in its
- * constructor) — same late-binding reason as AppDeps.events. Under the modern
- * skin nothing calls these; they are harmless no-ops if the window is gone.
- */
-export function windowControlHandlers(
-	getWindow: () => BrowserWindow | undefined,
-	/**
-	 * What the title bar's X does. Defaults to a raw `win.close()`. Editor
-	 * windows MUST pass their confirmed-close hook instead — the native close
-	 * is not cancellable, so a raw close there would skip the dirty prompt
-	 * (see gotchas.md "Window `close` is not cancellable").
-	 */
-	onClose: (win: BrowserWindow | undefined) => void = (win) => win?.close(),
-) {
-	return {
-		windowMinimize: () =>
-			wrap(() => {
-				getWindow()?.minimize();
-				return {};
-			}),
-
-		windowToggleMaximize: () =>
-			wrap(() => {
-				const win = getWindow();
-				if (!win) return { maximized: false };
-				// isMaximized is a synchronous FFI read, so this stays one round trip
-				const next = !win.isMaximized();
-				if (next) win.maximize();
-				else win.unmaximize();
-				return { maximized: next };
-			}),
-
-		windowClose: () =>
-			wrap(() => {
-				onClose(getWindow());
-				return {};
-			}),
-
-		windowIsMaximized: () => wrap(() => ({ maximized: getWindow()?.isMaximized() ?? false })),
-
-		// ---- STOPGAP: synthesized resize ----
-		// A frameless GTK window has no resize borders, and electrobun exposes no
-		// native resize gesture (it has startWindowMove and nothing else — the
-		// shipped libNativeWrapper does not even link gtk_window_begin_resize_drag).
-		// So the webview drags its own handles and moves the frame itself. Both are
-		// synchronous FFI reads/writes, like isMaximized above, so each drag tick
-		// stays one round trip. DELETE WITH THE REST OF THE HACK — the checklist is
-		// in ui/src/app/skins/7like/window-resize/window-resize.ts.
-		windowGetFrame: () =>
-			wrap(() => getWindow()?.getFrame() ?? { x: 0, y: 0, width: 0, height: 0 }),
-
-		// Params are annotated from the schema rather than inferred: this factory
-		// returns a bare object literal, so it gets none of the contextual typing
-		// the inline handler sets inside defineRPC<AppRPC> enjoy.
-		windowSetFrame: ({
-			x,
-			y,
-			width,
-			height,
-		}: AppRPC["bun"]["requests"]["windowSetFrame"]["params"]) =>
-			wrap(() => {
-				getWindow()?.setFrame(x, y, width, height);
-				return {};
-			}),
-	};
-}
-
 /** Connection-store requests, shared by the main and manager window rpcs. */
 function connectionStoreHandlers(store: ConnectionStore, onChanged: () => void) {
 	return {
@@ -199,7 +121,6 @@ export function createAppRPC({
 	settings,
 	edits,
 	watcher,
-	mainWindow,
 	events,
 }: AppDeps) {
 	return BrowserView.defineRPC<AppRPC>({
@@ -297,9 +218,6 @@ export function createAppRPC({
 						return {};
 					}),
 
-				// ---- custom window chrome (win7 skin) ----
-				...windowControlHandlers(mainWindow),
-
 				// ---- connection store ----
 				...connectionStoreHandlers(store, () => events.connectionsChanged()),
 
@@ -429,8 +347,6 @@ export interface EditorRpcHooks {
 	onSaved: () => void;
 	/** Webview resolved its dirty prompt: close without the native fallback. */
 	onCloseConfirmed: () => void;
-	/** This window, for the win7 title-bar controls (late-bound like the rest). */
-	window: () => BrowserWindow | undefined;
 }
 
 /**
@@ -466,12 +382,6 @@ export function createEditorRPC(
 						hooks.onCloseConfirmed();
 						return {};
 					}),
-
-				// win7 skin: this window is frameless, so the webview draws the
-				// chrome. The X routes through onCloseConfirmed (suppressPrompt +
-				// close), exactly like editorClose — the editor UI runs its dirty
-				// prompt BEFORE calling this, same as the ⌘W path.
-				...windowControlHandlers(hooks.window, () => hooks.onCloseConfirmed()),
 			},
 			messages: {
 				editorState: (state) => hooks.onDraft(state),
@@ -487,8 +397,6 @@ export interface ManagerRpcHooks {
 	onConnect: (id: string) => void;
 	onOpenStack: (id: string) => void;
 	onClose: () => void;
-	/** This window, for the win7 title-bar controls (late-bound like the rest). */
-	window: () => BrowserWindow | undefined;
 }
 
 /** RPC for the single connection-manager window (per-window instance). */
@@ -521,10 +429,6 @@ export function createManagerRPC(
 						hooks.onClose();
 						return {};
 					}),
-
-				// win7 skin: frameless window, webview-drawn chrome. The X reuses
-				// the managerClose path so the modal bookkeeping still runs.
-				...windowControlHandlers(hooks.window, () => hooks.onClose()),
 			},
 		},
 	});