feat(notes): attach selected Notes/Todos as Agent context (#6495)

* feat: add Notes and Todos as agent chat context

- Send selected Note/Todo IDs from the Notes UI
- Load selected notes with owner scoping in chat routes
- Format note content and checklist items for the model
- Inject selected notes as untrusted chat context
- Add a selected-context indicator beside Shell Access
- Keep selected context associated with the active chat session

* Improved selected notes context handling and discouragin redundant note lookup and permission requests

* Fix selected notes UI when switching chats

* fix(notes): harden selected context lifecycle and validation

---------

Co-authored-by: Alexandre Teixeira <111787685+alteixeira20@users.noreply.github.com>

tests/test_selected_notes_context.py

@@ -0,0 +1,28 @@
+"""Regression tests for untrusted selected-note ID parsing."""
+import json
+import pytest
+from fastapi import HTTPException
+from routes.chat_routes import _parse_selected_note_ids
+
+
+@pytest.mark.parametrize("raw,expected", [
+    (None, []),
+    ("", []),
+    ("[]", []),
+    ('["one", "two", "one"]', ["one", "two"]),
+])
+def test_selected_note_ids_valid(raw, expected):
+    assert _parse_selected_note_ids(raw) == expected
+
+
+@pytest.mark.parametrize("raw", [
+    "42", "true", "null", '{"id":"a"}',
+    '["one", 5]', '["one", null]', '["one", false]',
+    '[""]', '[" "]', '["one", {}]',
+    "not json", json.dumps(["a"] * 51),
+    json.dumps(["a" * 129]), " " * 8193,
+])
+def test_selected_note_ids_rejected(raw):
+    with pytest.raises(HTTPException) as exc:
+        _parse_selected_note_ids(raw)
+    assert exc.value.status_code == 400