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/electrum/scripthash.py

@@ -0,0 +1,15 @@
+import hashlib
+
+from embit.script import Script
+
+
+def address_to_scripthash(address: str) -> str:
+    """Electrum protocol scripthash: sha256(scriptPubKey), byte-reversed, hex.
+
+    Uses `.data` (the raw scriptPubKey bytes), not `.serialize()` — the latter
+    prefixes a compact-size length byte meant for embedding the script as pushdata
+    elsewhere (e.g. a P2SH redeemScript), which is not part of the actual on-chain
+    output script and produces a wrong (unmatchable) scripthash if used here.
+    """
+    script_pubkey = Script.from_address(address).data
+    return hashlib.sha256(script_pubkey).digest()[::-1].hex()