Move settings into a standalone Settings window

The tab-bar popover had outgrown itself. Settings now open in their own
native window (a fourth window kind, built like the connection manager but
not modal): a sidebar with Appearance, Transfers, Editor, File list and
About, holding every popover row plus the visible-columns choice. Each
control is an ordinary settings save, so the other windows follow live
while it stays open.

The gear button in the tab bar, Ctrl+, and the macOS app menu's
"Settings..." (Cmd+,) open it. On macOS Cmd+W arrives as the main window's
close-tab menu action, so bun closes the focused Settings window first
instead of a main-window tab.

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

src/bun/rpc-handlers.ts

@@ -31,6 +31,7 @@ export interface AppDeps {
 		openEditor: (ctx: EditorOpenContext) => void;
 		settingsChanged: (settings: AppSettings) => void;
 		openConnectionManager: () => void;
+		openSettings: () => void;
 		showAbout: () => void;
 	};
 }
@@ -130,6 +131,28 @@ const pickKeyFileHandler = () =>
 		return { path };
 	});
 
+/** External-editor picker, shared by the main and settings window rpcs. */
+const pickEditorAppHandler = () =>
+	wrap(async () => {
+		// PORTABILITY: apps live in different places per OS
+		const { homedir } = await import("node:os");
+		const [startingFolder, allowedFileTypes] =
+			process.platform === "darwin"
+				? ["/Applications", "app"]
+				: process.platform === "win32"
+					? [process.env.ProgramFiles ?? "C:\\Program Files", "exe"]
+					: [homedir(), "*"];
+		const picked = await Utils.openFileDialog({
+			startingFolder,
+			allowedFileTypes,
+			canChooseFiles: true,
+			canChooseDirectory: false,
+			allowsMultipleSelection: false,
+		});
+		const path = picked.find((p) => p.trim().length > 0) ?? null;
+		return { path };
+	});
+
 export function createAppRPC({
 	registry,
 	engine,
@@ -257,26 +280,7 @@ export function createAppRPC({
 				editExternal: ({ sessionId, path }) =>
 					wrap(() => edits.editExternal(sessionId, path)),
 
-				pickEditorApp: () =>
-					wrap(async () => {
-						// PORTABILITY: apps live in different places per OS
-						const { homedir } = await import("node:os");
-						const [startingFolder, allowedFileTypes] =
-							process.platform === "darwin"
-								? ["/Applications", "app"]
-								: process.platform === "win32"
-									? [process.env.ProgramFiles ?? "C:\\Program Files", "exe"]
-									: [homedir(), "*"];
-						const picked = await Utils.openFileDialog({
-							startingFolder,
-							allowedFileTypes,
-							canChooseFiles: true,
-							canChooseDirectory: false,
-							allowsMultipleSelection: false,
-						});
-						const path = picked.find((p) => p.trim().length > 0) ?? null;
-						return { path };
-					}),
+				pickEditorApp: pickEditorAppHandler,
 
 				pickKeyFile: pickKeyFileHandler,
 
@@ -318,6 +322,13 @@ export function createAppRPC({
 						return {};
 					}),
 
+				// ---- settings window ----
+				openSettings: () =>
+					wrap(async () => {
+						events.openSettings();
+						return {};
+					}),
+
 				showAbout: () =>
 					wrap(async () => {
 						events.showAbout();
@@ -449,3 +460,28 @@ export function createManagerRPC(
 		},
 	});
 }
+
+export interface SettingsRpcHooks {
+	/** Every edit here is a settings save — rebroadcast it to the other windows. */
+	onSettingsSaved: (next: AppSettings) => void;
+	showAbout: () => void;
+}
+
+/** RPC for the single Settings window (per-window instance). */
+export function createSettingsRPC(deps: { settings: SettingsStore }, hooks: SettingsRpcHooks) {
+	return BrowserView.defineRPC<AppRPC>({
+		maxRequestTime: MAX_REQUEST_TIME_MS,
+		handlers: {
+			requests: {
+				getSettings: () => wrap(async () => ({ settings: await deps.settings.load() })),
+				saveSettings: saveSettingsHandler(deps.settings, hooks.onSettingsSaved),
+				pickEditorApp: pickEditorAppHandler,
+				showAbout: () =>
+					wrap(async () => {
+						hooks.showAbout();
+						return {};
+					}),
+			},
+		},
+	});
+}