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>

src/fabledassistant/models/__init__.py

@@ -40,3 +40,4 @@ from fabledassistant.models.share import NoteShare, ProjectShare  # noqa: E402,
 from fabledassistant.models.notification import Notification  # noqa: E402, F401
 from fabledassistant.models.rss_feed import RssFeed, RssItem  # noqa: E402, F401
 from fabledassistant.models.weather_cache import WeatherCache  # noqa: E402, F401
+from fabledassistant.models.api_key import ApiKey  # noqa: E402, F401

src/fabledassistant/models/api_key.py

@@ -0,0 +1,42 @@
+from datetime import datetime
+
+from sqlalchemy import DateTime, ForeignKey, Index, Integer, Text
+from sqlalchemy.orm import Mapped, mapped_column
+
+from fabledassistant.models import Base
+from fabledassistant.models.base import CreatedAtMixin
+
+
+class ApiKey(Base, CreatedAtMixin):
+    __tablename__ = "api_keys"
+
+    id: Mapped[int] = mapped_column(primary_key=True)
+    user_id: Mapped[int] = mapped_column(
+        Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    name: Mapped[str] = mapped_column(Text, nullable=False)
+    key_hash: Mapped[str] = mapped_column(Text, nullable=False, unique=True)
+    key_prefix: Mapped[str] = mapped_column(Text, nullable=False)
+    scope: Mapped[str] = mapped_column(Text, nullable=False)  # "read" or "write"
+    last_used_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+    revoked_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
+
+    __table_args__ = (
+        Index("ix_api_keys_user_id", "user_id"),
+        Index("ix_api_keys_key_hash", "key_hash"),
+    )
+
+    def to_dict(self) -> dict:
+        return {
+            "id": self.id,
+            "name": self.name,
+            "key_prefix": self.key_prefix,
+            "scope": self.scope,
+            "last_used_at": self.last_used_at.isoformat() if self.last_used_at else None,
+            "created_at": self.created_at.isoformat(),
+            "revoked_at": self.revoked_at.isoformat() if self.revoked_at else None,
+        }