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>

src/models/event.rs

@@ -0,0 +1,45 @@
+use serde::{Deserialize, Serialize};
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+#[serde(rename_all = "snake_case")]
+pub enum EventType {
+    Totw,
+    Seasonal,
+    Special,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct PackWeightBoost {
+    pub rarity: String,
+    pub multiplier: f64,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EventEffects {
+    pub pack_weight_boosts: Vec<PackWeightBoost>,
+    pub bonus_market_cards: Vec<String>,
+    pub unlocks_sbc_ids: Vec<String>,
+    pub unlocks_objective_ids: Vec<String>,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize)]
+pub struct EventDefinition {
+    pub id: String,
+    pub name: String,
+    pub description: String,
+    pub event_type: EventType,
+    pub starts_at: Option<String>,
+    pub expires_at: Option<String>,
+    pub is_manual: bool,
+    pub effects: EventEffects,
+}
+
+/// Event definition bundled with its current runtime active status.
+#[derive(Debug, Clone, Serialize)]
+pub struct EventWithStatus {
+    #[serde(flatten)]
+    pub definition: EventDefinition,
+    pub is_active: bool,
+    pub activated_at: Option<String>,
+    pub deactivated_at: Option<String>,
+}