Add auth foundation: sessions/tokens schema, Argon2 hashing, config

Two tables (sessions, user_tokens) + migration; only token *hashes* are stored, so a DB leak yields no usable credential. Argon2id password hashing and token primitives in app/core/security. Config and .env.example gain session/cookie/token TTLs, app base URL, and SMTP settings (twelve-factor). Migration verified reversible (drops the token_purpose enum) and matches the models.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Signed-off-by: Justin Paul <justin@jpaul.me>

backend/app/core/config.py

@@ -27,6 +27,22 @@ class Settings(BaseSettings):
         default="postgresql+asyncpg://provenance:provenance@localhost:5432/provenance",
     )
 
+    # --- Auth / sessions ---
+    session_ttl_days: int = 30
+    token_ttl_hours: int = 24  # email-verify / password-reset token lifetime
+    cookie_name: str = "provenance_session"
+    cookie_secure: bool = True  # set false for local http; true behind TLS
+    # Base URL used to build links in outbound email.
+    app_base_url: str = "http://localhost"
+
+    # --- Email (SMTP) ---
+    mailer: str = Field(default="console", description="console | smtp")
+    smtp_host: str | None = None
+    smtp_port: int = 587
+    smtp_username: str | None = None
+    smtp_password: str | None = None
+    smtp_from: str = "Provenance <no-reply@provenance.local>"
+
 
 @lru_cache
 def get_settings() -> Settings: