feat(economy): add /lottery - daily draw, weighted winner takes the pot

Buy tickets (200 coins each, max 100/draw); one winner is drawn daily at 21:00
Tallinn time weighted by ticket count and credited the whole pot. Coin-conserving
by design: each ticket's cost is deducted at purchase and the winner is minted
exactly the sum of all ticket spend - no shared pot record, so no cross-period
race. Ticket state lives per-user keyed by draw period (full scan only at draw
time and for the pot view).

- New lottery.py: TICKET_COST/MAX_TICKETS/DRAW_HOUR, pure period_for, and
  do_buy_ticket / get_lottery_state / do_lottery_draw. New lottery_tickets +
  lottery_period schema fields (period added to _TEXT_FIELDS).
- /lottery [kogus] command (view or buy) with full failure handling.
- Scheduled lottery_draw_daily loop in bot.py (both profiles; each draws its own
  collection), announcing to the optional LOTTERY_CHANNEL_ID (config + .env).

14 tests: period boundary, buy/accumulate/reset/caps/guards, pot state, draw
payout with coin conservation, and the more-tickets-wins-more weighting.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013VbAVsrZuYesea99mPMmPT

core/economy/store.py

@@ -155,6 +155,8 @@ class UserData(TypedDict, total=False):
     best_daily_streak: int
     lootboxes_opened: int
     achievements_earned: list         # ids of achievements already claimed
+    lottery_tickets: int              # tickets held for the current lottery period
+    lottery_period: str | None        # draw-date the held tickets count for (ISO date)
     heist_global_cd_until: float
     # Prestige system
     prestige_level: int
@@ -219,6 +221,8 @@ def _default_user() -> UserData:
         "best_daily_streak": 0,
         "lootboxes_opened": 0,
         "achievements_earned": [],
+        "lottery_tickets": 0,
+        "lottery_period": None,
         "heist_global_cd_until": 0.0,
         # ── Prestige ─────────────────────────────────────────────────────────
         "prestige_level":    0,