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/intent.py

@@ -77,8 +77,13 @@ Rules:
 - Infer reasonable defaults: birthdays and holidays are all-day + yearly recurring; "weekly meeting" is weekly recurring.
 - Use descriptive titles: "My Birthday" not just "Birthday", "Team Standup" not just "Meeting".
 - "add to", "update", "edit", "expand", "flesh out", "modify", "append to", "continue writing" a note → use update_note with query=<note title from context> and mode="append" for additions or mode="replace" for full rewrites.
+- "mark as done", "complete", "finish", "mark in progress", "start" a task → use update_note with status field.
+- "set priority", "change priority", "make it high priority" → use update_note with priority field.
+- "set due date", "move due date", "due on Friday" for a task → use update_note with due_date field.
+- "what are my overdue tasks", "show overdue", "tasks due today", "high priority tasks", "in progress tasks", "what's due this week" → use list_tasks with appropriate status/priority/due_before/due_after filters. For overdue, set due_before to today's date.
 - If a note was created earlier in the conversation and the user provides more content for it, use update_note (not create_note).
 - Use create_note ONLY when the user explicitly wants a brand new note that doesn't already exist.
+- "update", "change", "rename", "set due date on" a CalDAV todo → use update_todo.
 - "update", "change", "move", "reschedule" an event → use update_event.
 - "delete", "cancel", "remove" an event → use delete_event.
 - "which calendars", "list calendars", "my calendars" → use list_calendars.