feat(briefing): add Message.msg_metadata and RssItem.topics/classified_at columns

msg_metadata maps to the 'metadata' DB column ('metadata' is reserved
by SQLAlchemy Declarative API). to_dict() exposes the key as 'metadata'
for frontend compatibility.

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

src/fabledassistant/models/conversation.py

@@ -67,6 +67,9 @@ class Message(Base, CreatedAtMixin):
         Integer, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
     )
     tool_calls: Mapped[list | None] = mapped_column(JSONB, nullable=True)
+    # 'metadata' is reserved by SQLAlchemy Declarative — use msg_metadata as the
+    # Python attribute name, mapped to the 'metadata' DB column.
+    msg_metadata: Mapped[dict | None] = mapped_column("metadata", JSONB, nullable=True)
 
     conversation: Mapped["Conversation"] = relationship(back_populates="messages")
 
@@ -83,5 +86,6 @@ class Message(Base, CreatedAtMixin):
             "status": self.status,
             "context_note_id": self.context_note_id,
             "tool_calls": self.tool_calls,
+            "metadata": self.msg_metadata,
             "created_at": self.created_at.isoformat(),
         }

src/fabledassistant/models/rss_feed.py

@@ -1,6 +1,6 @@
 from datetime import datetime, timezone
 
-from sqlalchemy import DateTime, ForeignKey, Index, Integer, Text, UniqueConstraint
+from sqlalchemy import ARRAY, DateTime, ForeignKey, Index, Integer, Text, UniqueConstraint
 from sqlalchemy.orm import Mapped, mapped_column, relationship
 
 from fabledassistant.models import Base
@@ -49,6 +49,12 @@ class RssItem(Base):
     fetched_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
+    topics: Mapped[list[str]] = mapped_column(
+        ARRAY(Text), nullable=False, default=list, server_default="{}"
+    )
+    classified_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
 
     feed: Mapped["RssFeed"] = relationship(back_populates="items")
 
@@ -67,4 +73,6 @@ class RssItem(Base):
             "url": self.url,
             "published_at": self.published_at.isoformat() if self.published_at else None,
             "content": self.content,
+            "topics": self.topics or [],
+            "classified_at": self.classified_at.isoformat() if self.classified_at else None,
         }