Server persistence: EF Core profiles + coin ledger + authoritative rewards

- EF Core (SQLite dev / Postgres prod via config); ProfileRow JSON blob +
  LedgerRow audit; EnsureCreated at startup
- C# Gamification port (ranks/elo/coins/xp/achievements/titles) → server
  computes match rewards; ProfileService (get/update/plan/buyCoins/applyMatch)
- JWT endpoints: profile GET/PUT, plan, coins packs/buy, match/result;
  auth upserts the profile
- Tested end-to-end (buy + ranked win+kot persisted & server-computed)
- Client still mock-backed for now (wiring is the next step)

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitignore

@@ -50,4 +50,7 @@ next-env.d.ts
 [Bb]in/
 [Oo]bj/
 *.user
+*.db
+*.db-shm
+*.db-wal