fix(notifications): reserve grid space for overlay thumbnail so it can't overlap text

The thumbnail was 100px wide but its grid column only reserved 56px, so on
macOS the image spilled ~44px into the content column and overlapped the
title/body. Reserve a minmax(0, 100px) track for the image and make the
image fluid (width: 100%; max-width: 100px; aspect-ratio) so it shrinks to
fit on narrow notifications instead of overlapping the text.

src/core/services/overlay-visibility.test.ts

@@ -154,6 +154,63 @@ test('macOS keeps visible overlay hidden while tracker is not ready and emits on
   assert.ok(!calls.includes('show'));
 });
 
+test('macOS dismisses overlay loading OSD when tracker recovers', () => {
+  const { window, calls } = createMainWindowRecorder();
+  let trackerWarning = false;
+  const osdMessages: string[] = [];
+  const dismissedOsds: string[] = [];
+  let tracking = false;
+  let geometry: WindowTrackerStub['getGeometry'] extends () => infer T ? T : never = null;
+  const tracker: WindowTrackerStub = {
+    isTracking: () => tracking,
+    getGeometry: () => geometry,
+    isTargetWindowFocused: () => tracking,
+  };
+
+  const run = () =>
+    updateVisibleOverlayVisibility({
+      visibleOverlayVisible: true,
+      mainWindow: window as never,
+      windowTracker: tracker as never,
+      trackerNotReadyWarningShown: trackerWarning,
+      setTrackerNotReadyWarningShown: (shown: boolean) => {
+        trackerWarning = shown;
+      },
+      updateVisibleOverlayBounds: () => {
+        calls.push('update-bounds');
+      },
+      ensureOverlayWindowLevel: () => {
+        calls.push('ensure-level');
+      },
+      syncPrimaryOverlayWindowLayer: () => {
+        calls.push('sync-layer');
+      },
+      enforceOverlayLayerOrder: () => {
+        calls.push('enforce-order');
+      },
+      syncOverlayShortcuts: () => {
+        calls.push('sync-shortcuts');
+      },
+      isMacOSPlatform: true,
+      showOverlayLoadingOsd: (message: string) => {
+        osdMessages.push(message);
+      },
+      dismissOverlayLoadingOsd: () => {
+        dismissedOsds.push('dismiss');
+      },
+    } as never);
+
+  run();
+  tracking = true;
+  geometry = { x: 0, y: 0, width: 1280, height: 720 };
+  run();
+
+  assert.deepEqual(osdMessages, ['Overlay loading...']);
+  assert.deepEqual(dismissedOsds, ['dismiss']);
+  assert.equal(trackerWarning, false);
+  assert.ok(calls.includes('show-inactive'));
+});
+
 test('tracked non-macOS overlay stays hidden while tracker is not ready', () => {
   const { window, calls } = createMainWindowRecorder();
   let trackerWarning = false;