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

.env.example

@@ -31,6 +31,12 @@ BIRTHDAY_CHANNEL_ID=
 # How many days before a birthday the on-join check counts as "coming up"
 BIRTHDAY_WINDOW_DAYS=7
 
+# Channel ID where the daily lottery draw result is announced (optional - the
+# draw still runs and pays the winner if unset; per-profile like BIRTHDAY_CHANNEL)
+LOTTERY_CHANNEL_ID_DEV=
+LOTTERY_CHANNEL_ID_ECONOMY=
+LOTTERY_CHANNEL_ID=
+
 # PocketBase backend (https://pocketbase.io)
 PB_URL=http://127.0.0.1:8090
 PB_ADMIN_EMAIL=admin@example.com