v1.2: overwrite confirm, transfer speed/ETA, settings + themes, fused macOS titlebar

- Overwrite confirmation: name-collision detection before enqueue; dialog shows
  source vs destination (size, mtime, 'newer' badge) with per-item Skip/Replace
  and batch Skip all / Replace all; type mismatches auto-skip with a toast;
  cancel aborts the whole operation
- Transfer speed + ETA: UI computes smoothed bytes/sec from progress deltas
  (callback bus makes deltas meaningful); shown in the expanded queue rows and
  the status-bar summary; unit follows the speed-unit setting
- Settings: bun-side SettingsStore (settings.json, 0600, atomic) + get/save RPC;
  SettingsService; gear popover on the tab row (theme segmented control, speed
  unit); persisted across restarts
- Light theme: data-theme on <html> drives token overrides; absent = follow OS
- macOS fused titlebar: hiddenInset + trafficLightOffset, tab row becomes the
  draggable titlebar (app-region drag/no-drag classes); other platforms keep a
  separate titlebar (gated by a platform value injected via window preload)
- README: known-issues note for the upstream Bun/Electrobun FFI crash

Verified: tsc + ui build clean; SettingsStore roundtrip + 0600 headless;
app boots and the UI fetches settings over RPC at startup.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/bun/index.ts

@@ -3,6 +3,7 @@ import { BRANDING } from "../shared/branding";
 import { SessionRegistry } from "./fs/registry";
 import { createAppRPC } from "./rpc-handlers";
 import { ConnectionStore } from "./store/connections";
+import { SettingsStore } from "./store/settings";
 import { TransferEngine } from "./transfers/engine";
 
 const PROD_URL = "views://app/index.html";
@@ -28,10 +29,13 @@ async function getMainViewUrl(): Promise<string> {
 const registry = new SessionRegistry();
 const engine = new TransferEngine(registry);
 const store = new ConnectionStore();
+const settings = new SettingsStore();
 const events = { sessionClosed: (_info: { sessionId: string; reason: string }) => {} };
-const rpc = createAppRPC({ registry, engine, store, events });
+const rpc = createAppRPC({ registry, engine, store, settings, events });
 const url = await getMainViewUrl();
 
+const isMac = process.platform === "darwin";
+
 new BrowserWindow({
 	title: BRANDING.appName,
 	url,
@@ -41,6 +45,14 @@ 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 } }
+		: {}),
+	// lets the UI pick the fused layout before first paint
+	preload: `window.__BUNSCP_PLATFORM=${JSON.stringify(process.platform)};`,
 	rpc,
 });