Move history to sidebar, simplify task assist, add content deduplication

- VersionHistorySection.vue: new sidebar component — collapsible timestamp list,
  click any snapshot to see inline diff + Restore/Back; replaces the modal
- NoteEditorView: remove History toolbar button + HistoryPanel modal, add
  VersionHistorySection at bottom of sidebar
- TaskEditorView: remove floating overlay assist panel + toggle button; add
  Writing Assistant section in sidebar matching note editor (scope selector,
  instruction textarea, generate/proofread/accept/reject); main area now shows
  streaming preview and DiffView like note editor; add VersionHistorySection
- note_versions.py: add content deduplication before time-gap check — identical
  body + title + tags skips snapshot regardless of interval (git semantics)

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

src/fabledassistant/services/note_versions.py

@@ -18,16 +18,24 @@ async def create_version(
     user_id: int, note_id: int, body: str, title: str, tags: list[str] | None = None
 ) -> NoteVersion | None:
     async with async_session() as session:
-        # Skip if a recent snapshot already exists within the minimum interval.
+        # Fetch the most recent snapshot once for both checks.
         recent = await session.execute(
-            select(NoteVersion.created_at)
+            select(NoteVersion)
             .where(NoteVersion.note_id == note_id, NoteVersion.user_id == user_id)
             .order_by(NoteVersion.created_at.desc())
             .limit(1)
         )
-        last_at = recent.scalar_one_or_none()
-        if last_at is not None:
-            # created_at is stored with timezone; ensure comparison is tz-aware
+        last = recent.scalars().first()
+        if last is not None:
+            # Skip if content is identical — no change, no snapshot (git semantics).
+            if (
+                last.body == body
+                and last.title == title
+                and sorted(last.tags or []) == sorted(tags or [])
+            ):
+                return None
+            # Skip if within the minimum interval to prevent rapid-fire autosave snapshots.
+            last_at = last.created_at
             if last_at.tzinfo is None:
                 last_at = last_at.replace(tzinfo=timezone.utc)
             age = (datetime.now(timezone.utc) - last_at).total_seconds()