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/rpc-handlers.ts

@@ -4,6 +4,7 @@ import type { Result } from "../shared/types";
 import type { SessionRegistry } from "./fs/registry";
 import { SftpProvider } from "./fs/sftp";
 import type { ConnectionStore } from "./store/connections";
+import type { SettingsStore } from "./store/settings";
 import type { TransferEngine } from "./transfers/engine";
 import { removeRecursive } from "./transfers/walk";
 
@@ -15,6 +16,7 @@ export interface AppDeps {
 	registry: SessionRegistry;
 	engine: TransferEngine;
 	store: ConnectionStore;
+	settings: SettingsStore;
 	/** Assigned after the rpc object exists (it needs rpc.send). */
 	events: { sessionClosed: (info: { sessionId: string; reason: string }) => void };
 }
@@ -27,7 +29,7 @@ async function wrap<T extends object>(fn: () => Promise<T> | T): Promise<Result<
 	}
 }
 
-export function createAppRPC({ registry, engine, store, events }: AppDeps) {
+export function createAppRPC({ registry, engine, store, settings, events }: AppDeps) {
 	return BrowserView.defineRPC<AppRPC>({
 		maxRequestTime: MAX_REQUEST_TIME_MS,
 		handlers: {
@@ -135,6 +137,15 @@ export function createAppRPC({ registry, engine, store, events }: AppDeps) {
 						await store.deleteFolder(id);
 						return {};
 					}),
+
+				// ---- settings ----
+				getSettings: () => wrap(async () => ({ settings: await settings.load() })),
+
+				saveSettings: ({ settings: next }) =>
+					wrap(async () => {
+						await settings.save(next);
+						return {};
+					}),
 			},
 		},
 	});