Implement full MVP: auth, HD wallet, Electrum client, deposits, bets, round/draw engine, payout, withdrawals, RBF, admin+audit

All 10 build-order stages complete and unit-tested (49 tests). Verified live on
mainnet: registration/address derivation, deposit crediting, a real 10 PLM bet
(broadcast + confirmed + change credited). A full round close->draw->payout
cycle was triggered live and was in progress at commit time. Withdrawal and RBF
bump are unit-tested but not yet exercised against a live broadcast. Known gaps
(scheduler doesn't resume mid-flight rounds after restart, payout has no retry,
no deployment setup, etc.) are documented in CLAUDE.md.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/rounds/service.py

@@ -0,0 +1,27 @@
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
+from app.db.models import Round
+
+_ACTIVE_STATUSES = ("open", "closing", "drawing", "paying_out")
+
+
+async def get_active_round(session: AsyncSession) -> Round | None:
+    """The round currently in progress (in any non-closed state), if any. Rounds
+    never overlap: a new round only opens once the previous one is fully closed
+    (payout confirmed, or no participants to pay out)."""
+    return await session.scalar(select(Round).where(Round.status.in_(_ACTIVE_STATUSES)).order_by(Round.id.desc()))
+
+
+async def open_new_round_if_needed(session: AsyncSession) -> Round:
+    """Returns the active round if one exists (whatever its status), otherwise
+    opens a fresh one. Callers that need to attach a bet must additionally check
+    the returned round's status == "open" — a round in closing/drawing/paying_out
+    isn't accepting new bets, but a new round can't open until it's done."""
+    active = await get_active_round(session)
+    if active is not None:
+        return active
+    round_ = Round(status="open")
+    session.add(round_)
+    await session.flush()
+    return round_