feat(05-01): add push_subscriptions table + calendar_events.title column; VAPID env wiring

- schema.ts: new pushSubscriptions mysqlTable (user_id FK cascade, endpoint unique, p256dh, auth)
- schema.ts: add nullable title varchar(500) to calendarEvents after rawVevent (D-02/NOTIF-01)
- 0003_same_xavin.sql: CREATE TABLE push_subscriptions + ALTER calendar_events ADD title
- migration applied to dev DB via db:generate + db:migrate (NOT db:push per anti-pattern)
- docker-compose.yml: inject VAPID_PUBLIC_KEY/PRIVATE_KEY/SUBJECT into api environment block
- .env.example: document all three VAPID vars with placeholders + generation instructions

apps/api/src/db/migrations/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1781029240528,
       "tag": "0002_yielding_mattie_franklin",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "5",
+      "when": 1781052360194,
+      "tag": "0003_same_xavin",
+      "breakpoints": true
     }
   ]
 }