feat(win): W2/UX19 persist window placement, W10 taskbar flash; tick W11

- W2/UX19: windowState.ts persists the window's normal bounds + maximized flag to
  <userData>/window-state.json (no new dep); createWindow restores from it with a
  screen.getAllDisplays() visibility guard so it never reopens off a disconnected
  monitor. Debounced save on resize/move + save on close (which may hide to tray).
- W10: notify() flashFrame(true)s the taskbar when a completion/failure lands while
  the window is unfocused/minimized (Windows clears the flash on focus).
- W11: already implemented (badge.ts overlay dot + setOverlayIcon) — ticked.

typecheck + 268 tests + eslint + prettier green. (Window restore + flash want a
live quit/relaunch confirm.)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/main/windowState.ts

@@ -0,0 +1,82 @@
+import { app, screen, type BrowserWindow, type Rectangle } from 'electron'
+import { join } from 'path'
+import { readFileSync, writeFileSync } from 'fs'
+import { logger } from './logger'
+
+/**
+ * Persist and restore the main window's size / position / maximized state across
+ * launches (W2 / UX19) — Windows apps are expected to reopen where you left them.
+ * Stored as one small JSON object in `<userData>/window-state.json`; a disconnected
+ * monitor is handled by a visibility check so the window can never restore off-screen.
+ */
+
+interface WindowState {
+  bounds: Rectangle
+  maximized: boolean
+}
+
+// Matches the createWindow() defaults; used on first run and when a saved position
+// is no longer on any connected display.
+const DEFAULT_SIZE = { width: 920, height: 700 }
+
+function stateFile(): string {
+  return join(app.getPath('userData'), 'window-state.json')
+}
+
+function readState(): WindowState | null {
+  try {
+    const s = JSON.parse(readFileSync(stateFile(), 'utf8')) as Partial<WindowState>
+    if (s?.bounds && typeof s.bounds.width === 'number' && typeof s.bounds.height === 'number') {
+      return { bounds: s.bounds as Rectangle, maximized: !!s.maximized }
+    }
+  } catch {
+    /* first run or corrupt — fall back to defaults */
+  }
+  return null
+}
+
+/** True when `b` overlaps the work area of some connected display (i.e. is reachable). */
+function isOnSomeDisplay(b: Rectangle): boolean {
+  return screen.getAllDisplays().some((d) => {
+    const wa = d.workArea
+    return (
+      b.x < wa.x + wa.width &&
+      b.x + b.width > wa.x &&
+      b.y < wa.y + wa.height &&
+      b.y + b.height > wa.y
+    )
+  })
+}
+
+/**
+ * The bounds + maximized flag to open the window with. Returns just a size (Electron
+ * then centers it) when there's no usable saved position — first run, or the saved
+ * monitor is gone.
+ */
+export function initialWindowState(): {
+  width: number
+  height: number
+  x?: number
+  y?: number
+  maximized: boolean
+} {
+  const saved = readState()
+  if (saved && isOnSomeDisplay(saved.bounds)) {
+    return { ...saved.bounds, maximized: saved.maximized }
+  }
+  return { ...DEFAULT_SIZE, maximized: saved?.maximized ?? false }
+}
+
+/**
+ * Persist the window's current *normal* bounds (un-maximized) + maximized flag.
+ * Best-effort; a write failure is logged, never thrown. Callers should debounce.
+ */
+export function saveWindowState(win: BrowserWindow): void {
+  if (win.isDestroyed() || win.isMinimized()) return
+  try {
+    const state: WindowState = { bounds: win.getNormalBounds(), maximized: win.isMaximized() }
+    writeFileSync(stateFile(), JSON.stringify(state))
+  } catch (e) {
+    logger.warn('failed to save window state', e)
+  }
+}