Session UX: tray-controlled recording, no per-shot window hiding

Users couldn't click into the app mid-session: every automatic capture
hid the window for the shot, so it vanished under the cursor. Under
WSLg minimize() is a no-op and isFocused() sticks true, so neither can
be used for control.

- Sessions now hide the window once at start and show a red tray icon
  with Capture now / Pause-Resume / Open StepForge (auto-pauses) /
  Finish; finishing or quitting restores/cleans up properly
- Opening the app from the tray pauses capture; resuming tucks the
  window away again
- Automatic captures skip while the cursor is over a visible StepForge
  window (cursor-based, not focus-based, due to WSLg sticky focus)
- Per-shot latency reduced: with the window already hidden the 350 ms
  hide-repaint wait is skipped entirely
- OS notification announces the session; self-tests updated and green

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

app/main.js

@@ -105,6 +105,10 @@ function createWindow() {
         try {
           const guide = store.createGuide({ title: 'hotkey selftest' });
           capture.startSession(guide.guideId, { intervalSec: 0 });
+          // Sessions hide the window while recording; do it immediately here
+          // instead of waiting out the toast-grace delay.
+          mainWindow.hide();
+          await new Promise((res) => setTimeout(res, 400));
           const results = [];
           for (let i = 0; i < 3; i++) {
             const r = await capture.hotkeyCapture();
@@ -486,6 +490,11 @@ if (!gotLock) {
 
   app.on('will-quit', () => {
     globalShortcut.unregisterAll();
+    if (capture) {
+      // Targeted cleanup (not finishSession — that re-shows the window).
+      capture.stopClickWatcher();
+      capture.destroySessionTray();
+    }
     // clean preview temp files on close
     try {
       for (const entry of fs.readdirSync(store.tempDir)) {