feat(analytics): opt-in usage analytics with server ingest and settings toggle

- Server: POST /api/analytics endpoint with per-IP rate limit (5/min),
  batch validation (≤50 events, event_type regex, UUID dedup, clock check),
  INSERT OR IGNORE for idempotency, and migration 004_analytics.sql
- Client (solitaire_data): AnalyticsClient with in-memory Mutex buffer,
  UUID session_id per launch, async flush via background task
- Engine: AnalyticsPlugin records game_won, game_forfeit, game_start,
  achievement_unlocked; flushes immediately on game-end, every 60 s otherwise
- Settings UI: Privacy section with ON/OFF toggle, hidden in local-only mode
- Default: analytics_enabled = false (explicit opt-in required)

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

.sqlx/query-f23630e78ae88e72d7930184f7cd8fc67e71f3930609f1cf14061d35d6de8ec3.json

@@ -0,0 +1,12 @@
+{
+  "db_name": "SQLite",
+  "query": "INSERT OR IGNORE INTO analytics_events\n               (id, user_id, session_id, event_type, payload, client_time, received_at)\n               VALUES (?, ?, ?, ?, ?, ?, ?)",
+  "describe": {
+    "columns": [],
+    "parameters": {
+      "Right": 7
+    },
+    "nullable": []
+  },
+  "hash": "f23630e78ae88e72d7930184f7cd8fc67e71f3930609f1cf14061d35d6de8ec3"
+}