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>

.env.example

@@ -0,0 +1,20 @@
+DATABASE_URL=sqlite+aiosqlite:///./plm_lottery.db
+
+ELECTRUM_HOST=santantonio.sytes.net
+ELECTRUM_PORT=50002
+ELECTRUM_USE_SSL=true
+
+# Fernet key protecting the master xprv at rest. Generate with:
+#   python -c "from cryptography.fernet import Fernet; print(Fernet.generate_key().decode())"
+XPRV_ENCRYPTION_KEY=
+MASTER_KEY_PATH=./master.xprv.enc
+
+# Random secret for JWT session signing. Generate with:
+#   python -c "import secrets; print(secrets.token_urlsafe(32))"
+JWT_SECRET=
+
+# Bearer token required on the admin endpoints (X-Admin-Token header). Generate with:
+#   python -c "import secrets; print(secrets.token_urlsafe(32))"
+ADMIN_TOKEN=
+
+ROUND_DURATION_SECONDS=600