feat(schema): add note.description and note.consolidated_at

Spec: docs/superpowers/specs/2026-05-13-task-as-durable-record-design.md

- description: user-stated goal / initial context for tasks (NULL for
  knowledge notes).
- consolidated_at: timestamp of the most recent auto-summary pass (NULL
  until first consolidation).
- Migration 0044 backfills description from body for existing rows where
  status IS NOT NULL (i.e. tasks). Body left in place; first consolidation
  pass will overwrite it.

src/fabledassistant/models/note.py

@@ -32,6 +32,10 @@ class Note(Base, TimestampMixin):
     )
     title: Mapped[str] = mapped_column(Text, default="")
     body: Mapped[str] = mapped_column(Text, default="")
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    consolidated_at: Mapped[datetime | None] = mapped_column(
+        DateTime(timezone=True), nullable=True
+    )
     tags: Mapped[list[str]] = mapped_column(ARRAY(Text), default=list)
     parent_id: Mapped[int | None] = mapped_column(
         Integer, ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
@@ -81,6 +85,10 @@ class Note(Base, TimestampMixin):
             "id": self.id,
             "title": self.title,
             "body": self.body,
+            "description": self.description,
+            "consolidated_at": (
+                self.consolidated_at.isoformat() if self.consolidated_at else None
+            ),
             "tags": self.tags or [],
             "parent_id": self.parent_id,
             "project_id": self.project_id,