Scaffold project layout, DB schema and settings

Package skeleton, pyproject/alembic config, env-driven settings
(app/config.py), and the SQLAlchemy models + initial Alembic migration
covering users, UTXO events, rounds/participants, round config,
pending transactions, withdrawals and the audit log.

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

app/config.py

@@ -0,0 +1,29 @@
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore")
+
+    database_url: str = "sqlite+aiosqlite:///./plm_lottery.db"
+
+    electrum_host: str = "santantonio.sytes.net"
+    electrum_port: int = 50002
+    electrum_use_ssl: bool = True
+
+    xprv_encryption_key: str = ""
+    master_key_path: str = "./master.xprv.enc"
+    jwt_secret: str = ""
+    jwt_algorithm: str = "HS256"
+    jwt_expire_minutes: int = 60 * 24
+    admin_token: str = ""
+
+    round_duration_seconds: int = 600
+
+    bet_amount_sats: int = 10 * 100_000_000
+    min_amount_sats: int = 1 * 100_000_000
+    confirmations_required: int = 1
+    fee_rate_sat_vb: int = 1
+    rbf_timeout_seconds: int = 900
+
+
+settings = Settings()