feat: add ApiKey model and migration 0027

Adds api_keys table with user_id FK, key_hash, key_prefix, scope
(read/write), last_used_at, revoked_at. SHA-256 hashed, soft-delete.

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

alembic/versions/0027_add_api_keys.py

@@ -0,0 +1,34 @@
+"""add api_keys table
+
+Revision ID: 0027
+Revises: 0026
+Create Date: 2026-03-23
+"""
+from alembic import op
+import sqlalchemy as sa
+
+revision = "0027"
+down_revision = "0026"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.create_table(
+        "api_keys",
+        sa.Column("id", sa.Integer(), primary_key=True),
+        sa.Column("user_id", sa.Integer(), sa.ForeignKey("users.id", ondelete="CASCADE"), nullable=False),
+        sa.Column("name", sa.Text(), nullable=False),
+        sa.Column("key_hash", sa.Text(), nullable=False, unique=True),
+        sa.Column("key_prefix", sa.Text(), nullable=False),
+        sa.Column("scope", sa.Text(), nullable=False),
+        sa.Column("last_used_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("revoked_at", sa.DateTime(timezone=True), nullable=True),
+        sa.Column("created_at", sa.DateTime(timezone=True), server_default=sa.func.now(), nullable=False),
+    )
+    op.create_index("ix_api_keys_user_id", "api_keys", ["user_id"])
+    op.create_index("ix_api_keys_key_hash", "api_keys", ["key_hash"])
+
+
+def downgrade() -> None:
+    op.drop_table("api_keys")