Merge tasks into notes: a task is just a note with task attributes

A task is now a note with status/priority/due_date columns set (status IS NOT NULL).
This eliminates the separate tasks table, companion note system, cascade deletes,
bidirectional title sync, and _skip_cascade flags.

Migration (0004):
- Add status, priority, due_date columns to notes table
- Migrate task data from companion notes and orphan tasks
- Drop tasks table and old enum types

Backend:
- models/note.py: Add TaskStatus/TaskPriority enums, task columns, is_task property
- models/task.py: Deleted (merged into note.py)
- models/__init__.py: Re-export enums from note.py, remove Task import
- services/notes.py: Remove companion/cascade logic, add is_task filter,
  convert_note_to_task, convert_task_to_note, simplified backlinks
- services/tasks.py: Rewritten as thin wrappers around notes service
- routes/notes.py: Add is_task filter (default false), task fields in CRUD,
  convert-to-note endpoint
- routes/tasks.py: description→body (with fallback), remove note_id filter

Frontend:
- types/note.ts: Add TaskStatus, TaskPriority, task fields to Note interface
- types/task.ts: Task is now a re-export alias for Note
- stores/notes.ts: Simplify convertToTask, add convertToNote
- stores/tasks.ts: description→body in createTask/updateTask
- TaskEditorView: description→body, remove companion note UI
- TaskViewerView: description→body, remove companion note link, add Convert to Note
- NoteViewerView: Remove companion task UI, simplify convert-to-task
- TaskCard: description→body, non-null assertions for status/priority

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

src/fabledassistant/models/note.py

@@ -1,12 +1,26 @@
-from datetime import datetime, timezone
+import enum
+from datetime import date, datetime, timezone
 
-from sqlalchemy import DateTime, ForeignKey, Index, Text
+from sqlalchemy import Date, DateTime, Index, Text
 from sqlalchemy.dialects.postgresql import ARRAY
 from sqlalchemy.orm import Mapped, mapped_column
 
 from fabledassistant.models import Base
 
 
+class TaskStatus(str, enum.Enum):
+    todo = "todo"
+    in_progress = "in_progress"
+    done = "done"
+
+
+class TaskPriority(str, enum.Enum):
+    none = "none"
+    low = "low"
+    medium = "medium"
+    high = "high"
+
+
 class Note(Base):
     __tablename__ = "notes"
 
@@ -15,8 +29,11 @@ class Note(Base):
     body: Mapped[str] = mapped_column(Text, default="")
     tags: Mapped[list[str]] = mapped_column(ARRAY(Text), default=list)
     parent_id: Mapped[int | None] = mapped_column(
-        ForeignKey("notes.id", ondelete="SET NULL"), nullable=True
+        nullable=True
     )
+    status: Mapped[str | None] = mapped_column(Text, nullable=True)
+    priority: Mapped[str | None] = mapped_column(Text, nullable=True)
+    due_date: Mapped[date | None] = mapped_column(Date, nullable=True)
     created_at: Mapped[datetime] = mapped_column(
         DateTime(timezone=True), default=lambda: datetime.now(timezone.utc)
     )
@@ -26,7 +43,14 @@ class Note(Base):
         onupdate=lambda: datetime.now(timezone.utc),
     )
 
-    __table_args__ = (Index("ix_notes_tags", "tags", postgresql_using="gin"),)
+    __table_args__ = (
+        Index("ix_notes_tags", "tags", postgresql_using="gin"),
+        Index("ix_notes_status", "status"),
+    )
+
+    @property
+    def is_task(self) -> bool:
+        return self.status is not None
 
     def to_dict(self) -> dict:
         return {
@@ -35,6 +59,10 @@ class Note(Base):
             "body": self.body,
             "tags": self.tags or [],
             "parent_id": self.parent_id,
+            "status": self.status,
+            "priority": self.priority,
+            "due_date": self.due_date.isoformat() if self.due_date else None,
+            "is_task": self.is_task,
             "created_at": self.created_at.isoformat(),
             "updated_at": self.updated_at.isoformat(),
         }