feat: Phase 5 — events system complete

Adds a data-driven event system (#47 schema, #48 activation, #49 TOTW):

- EventDefinition JSON schema (event_type, effects, date range, is_manual)
- data/events/totw_week1.json — TOTW event active by date range (2024–2030),
  injects 5 TOTW cards into the market as [EVENT] listings
- data/events/seasonal_events.json — Spring Festival and Icon Weekend,
  manual-activation-only example events
- migrations/0004_events.sql — events override table (NULL/1/0 per event)
- services/event — load_event_definitions, compute_is_active (date range +
  manual override), get_active_events, get_all_with_status, activate/deactivate
- routes/events — GET /events, GET /events/:id, POST .../activate, .../deactivate
- services/market::refresh_npc_listings now accepts event_defs, injects bonus
  market cards from active events at 2× premium price
- 5 new integration tests (events list, single, activate/deactivate cycle,
  404 on unknown, market injection verification); 19/19 passing

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

data/events/totw_week1.json

@@ -0,0 +1,25 @@
+[
+  {
+    "id": "totw_week1",
+    "name": "Team of the Week 1",
+    "description": "This week's TOTW is live! TOTW players appear in the transfer market at a premium and pack weights are boosted.",
+    "event_type": "totw",
+    "starts_at": "2024-01-01T00:00:00Z",
+    "expires_at": "2030-12-31T23:59:59Z",
+    "is_manual": false,
+    "effects": {
+      "pack_weight_boosts": [
+        { "rarity": "totw", "multiplier": 3.0 }
+      ],
+      "bonus_market_cards": [
+        "card_totw_001",
+        "card_totw_002",
+        "card_totw_003",
+        "card_totw_004",
+        "card_totw_005"
+      ],
+      "unlocks_sbc_ids": [],
+      "unlocks_objective_ids": []
+    }
+  }
+]