feat: web push notifications (VAPID)

- push_utils.py: subscription storage + send helper (auto-prunes 410 endpoints)
- routers/push.py: GET /api/push/vapid-key (public), POST/DELETE /api/push/subscribe
- sw.js: push event listener shows notification; notificationclick focuses/opens tab
- app.js: subscribe/unsubscribe flow + "Enable notifications" toggle in settings dropdown
- tools/notify.py: web_push orchestrator tool (user-level, no admin required)
- VAPID keys in .env; pywebpush added to requirements.txt

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cortex/tools/notify.py

@@ -67,6 +67,16 @@ async def email_send(to: str, subject: str, body: str) -> str:
     return "Failed to send email — check SMTP configuration in .env."
 
 
+async def web_push(title: str, body: str, url: str = "") -> str:
+    """Send a browser push notification to the current user's registered devices."""
+    import push_utils
+    username = get_user()
+    result = await push_utils.send_push(username, title, body, url)
+    if "error" in result:
+        return f"Push failed: {result['error']}"
+    return f"Push sent to {result['sent']} device(s) for {username} (pruned {result['pruned']} stale)."
+
+
 async def nc_talk_send(message: str) -> str:
     """Send a message to the user via their configured notification channel.
 
@@ -84,6 +94,24 @@ async def nc_talk_send(message: str) -> str:
 
 
 DECLARATIONS = [
+    types.FunctionDeclaration(
+        name="web_push",
+        description=(
+            "Send a browser push notification to the current user. Works even when the "
+            "Cortex tab is not open. Use for completing long tasks, reminders that fire "
+            "in the background, or anything the user should see immediately. "
+            "url is optional — if set, clicking the notification opens that URL."
+        ),
+        parameters=types.Schema(
+            type=types.Type.OBJECT,
+            properties={
+                "title": types.Schema(type=types.Type.STRING, description="Notification title (short)"),
+                "body":  types.Schema(type=types.Type.STRING, description="Notification body text"),
+                "url":   types.Schema(type=types.Type.STRING, description="Optional URL to open on click"),
+            },
+            required=["title", "body"],
+        ),
+    ),
     types.FunctionDeclaration(
         name="email_send",
         description=(