Add update_task fields, list_tasks, and update_todo tools

- update_note: extend with status/priority/due_date fields so task attributes
  can be changed via chat (mark done, set priority, move due date). body is now
  optional — task field updates work without touching content.
- list_tasks: new core tool with status/priority/due_before/due_after/limit
  filters backed by list_notes(is_task=True). Enables queries like
  "overdue tasks", "high priority tasks", "what's in progress".
- update_todo: new CalDAV tool to modify VTODO summary, due date, description,
  and priority — follows update_event pattern (modify component, rebuild ical,
  save). Completes the CalDAV todo CRUD suite.
- tools.py: add update_todo import + execute case (type: todo_updated)
- llm.py: add list_tasks and update_todo to available actions + guidance
- intent.py: routing rules for mark-done/priority/due-date → update_note,
  overdue/in-progress/high-priority queries → list_tasks, CalDAV todo updates
  → update_todo
- ToolCallCard.vue: tasks list block (linked titles + due + priority badges),
  todo_updated label, tool-task-priority CSS classes

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

src/fabledassistant/services/caldav.py

@@ -575,6 +575,81 @@ async def complete_todo(
     return await asyncio.to_thread(_complete)
 
 
+async def update_todo(
+    user_id: int,
+    query: str,
+    summary: str | None = None,
+    due: str | None = None,
+    description: str | None = None,
+    priority: int | None = None,
+    timezone: str | None = None,
+    calendar_name: str | None = None,
+) -> dict:
+    """Update a CalDAV todo matching the query."""
+    config = await get_caldav_config(user_id)
+    _check_config(config)
+    tz = timezone or config.get("caldav_timezone") or None
+
+    def _do_update():
+        client = _make_client(config)
+        cal_name = calendar_name or config.get("caldav_calendar_name", "")
+        calendar = _get_calendar(client, cal_name)
+        todos = calendar.todos(include_completed=True)
+
+        q = query.lower()
+        matches = []
+        for t in todos:
+            cal_obj = icalendar.Calendar.from_ical(t.data)
+            for component in cal_obj.walk():
+                if component.name == "VTODO":
+                    s = str(component.get("SUMMARY", ""))
+                    if q in s.lower():
+                        matches.append((t, component))
+
+        if not matches:
+            raise ValueError(f"No todo found matching '{query}'.")
+        if len(matches) > 3:
+            titles = [str(m[1].get("SUMMARY", "")) for m in matches]
+            raise ValueError(
+                f"Too many matches ({len(matches)}) for '{query}'. "
+                f"Be more specific. Found: {', '.join(titles[:10])}"
+            )
+
+        todo_obj, component = matches[0]
+
+        if summary:
+            component["SUMMARY"] = summary
+        if description is not None:
+            if "DESCRIPTION" in component:
+                del component["DESCRIPTION"]
+            component.add("description", description)
+        if priority is not None:
+            if "PRIORITY" in component:
+                del component["PRIORITY"]
+            component.add("priority", priority)
+        if due:
+            if "DUE" in component:
+                del component["DUE"]
+            try:
+                dt = datetime.fromisoformat(due)
+                dt = _apply_timezone(dt, tz)
+                component.add("due", dt)
+            except ValueError:
+                component.add("due", date_type.fromisoformat(due))
+
+        # Rebuild ical data and save
+        cal_data = icalendar.Calendar()
+        cal_data.add("prodid", "-//FabledAssistant//EN")
+        cal_data.add("version", "2.0")
+        cal_data.add_component(component)
+        todo_obj.data = cal_data.to_ical().decode("utf-8")
+        todo_obj.save()
+
+        return _parse_vtodo(component)
+
+    return await asyncio.to_thread(_do_update)
+
+
 async def delete_todo(
     user_id: int,
     query: str,