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

bot.py

@@ -336,6 +336,72 @@ async def before_birthday_daily():
     await bot.wait_until_ready()
 
 
+# ---------------------------------------------------------------------------
+# Daily lottery draw (Tallinn-time DRAW_HOUR:00)
+# ---------------------------------------------------------------------------
+async def _resolve_channel(channel_id: int):
+    """Best-effort fetch of a text channel by id (cache, then API)."""
+    if not channel_id:
+        return None
+    channel = bot.get_channel(channel_id)
+    if channel is None:
+        try:
+            channel = await bot.fetch_channel(channel_id)
+        except (discord.NotFound, discord.Forbidden, discord.HTTPException):
+            return None
+    return channel
+
+
+@tasks.loop(time=datetime.time(hour=economy.lottery.DRAW_HOUR, minute=0, tzinfo=TALLINN_TZ))
+async def lottery_draw_daily():
+    """Draw the day's lottery winner and announce it (if a channel is set)."""
+    period = datetime.datetime.now(TALLINN_TZ).date().isoformat()
+    try:
+        result = await economy.do_lottery_draw(period)
+    except Exception:
+        log.exception("Lottery draw failed for %s", period)
+        return
+    channel = await _resolve_channel(config.LOTTERY_CHANNEL_ID)
+    if result is None:
+        log.info("Lottery draw %s: no participants", period)
+        if channel:
+            try:
+                await channel.send(S.LOTTERY_UI["draw_none"])
+            except discord.HTTPException:
+                pass
+        return
+    if not result.get("ok"):
+        log.error("Lottery draw %s could not pay winner %s (pot %s)",
+                  period, result.get("winner_id"), result.get("pot"))
+        return
+    log.info("Lottery draw %s: winner %s won %s (%s/%s tickets)",
+             period, result["winner_id"], result["pot"],
+             result["winner_tickets"], result["total_tickets"])
+    if channel:
+        mention = f"<@{result['winner_id']}>"
+        embed = discord.Embed(
+            title=S.LOTTERY_UI["draw_title"],
+            description=S.LOTTERY_UI["draw_win"].format(
+                winner=mention,
+                pot=_coin(result["pot"]),
+                tickets=result["winner_tickets"],
+                total=result["total_tickets"],
+                chance=round(result["win_chance"] * 100, 1),
+                players=result["participants"],
+            ),
+            color=0xF4C430,
+        )
+        try:
+            await channel.send(content=mention, embed=embed)
+        except discord.HTTPException:
+            pass
+
+
+@lottery_draw_daily.before_loop
+async def before_lottery_draw_daily():
+    await bot.wait_until_ready()
+
+
 # ---------------------------------------------------------------------------
 # Rotating rich presence
 # ---------------------------------------------------------------------------
@@ -433,6 +499,11 @@ async def on_ready():
         birthday_daily.start()
         log.info("Birthday daily task started (fires 09:00 Tallinn time)")
 
+    # Start daily lottery draw (runs in every profile; each has its own collection)
+    if not lottery_draw_daily.is_running():
+        lottery_draw_daily.start()
+        log.info("Lottery draw task started (fires %02d:00 Tallinn time)", economy.lottery.DRAW_HOUR)
+
     # Start rotating rich presence
     if not _rotate_presence.is_running():
         _rotate_presence.start()