Add email-based password reset flow

Users who forget their password can now request a reset link via email.
Tokens are SHA-256 hashed before storage, expire after 1 hour, and
previous unused tokens are invalidated on new requests. The forgot-password
endpoint always returns success to prevent email enumeration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

alembic/versions/0011_add_password_reset_tokens.py

@@ -0,0 +1,25 @@
+"""Add password_reset_tokens table."""
+
+from alembic import op
+
+revision = "0011"
+down_revision = "0010"
+
+
+def upgrade() -> None:
+    op.execute("""
+        CREATE TABLE password_reset_tokens (
+            id SERIAL PRIMARY KEY,
+            user_id INTEGER NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+            token_hash TEXT NOT NULL UNIQUE,
+            expires_at TIMESTAMPTZ NOT NULL,
+            used BOOLEAN NOT NULL DEFAULT FALSE,
+            created_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+        )
+    """)
+    op.execute("CREATE INDEX ix_password_reset_tokens_token_hash ON password_reset_tokens (token_hash)")
+    op.execute("CREATE INDEX ix_password_reset_tokens_user_id ON password_reset_tokens (user_id)")
+
+
+def downgrade() -> None:
+    op.execute("DROP TABLE IF EXISTS password_reset_tokens")