fix(hooks): handle dict-key bracket notation in set_value / get_value

The Hook API previously rejected key strings like
'show_windows["Project Settings"]' (and silently returned None on
get). The test_live_gui_filedialog_regression test exercises exactly
this pattern to open the Project Settings window via the Hook API;
it was previously marked skip with "hook server doesn't handle the
dict-key bracket-notation syntax".

Fix in three small places:

1. src/app_controller.py:_handle_set_value
   If `item` is not in _settable_fields, try parsing it as
   `dict_name[<key>]` notation. If dict_name IS in _settable_fields
   and the current attr is a dict, set the inner key.

2. src/api_hooks.py:/api/gui/value (POST get_val)
   Mirror the parsing for the field-based get endpoint.

3. src/api_hook_client.py:ApiHookClient.get_value
   Mirror the parsing in the client so the dict-key syntax works
   through the state endpoint as well (which is what get_value
   actually calls by default).

Test fix:
- tests/test_live_gui_filedialog_regression.py: removed the
  @pytest.mark.skip marker; the underlying issue is now fixed.

Verified: 1/1 test passes (previously skipped).

src/api_hooks.py

@@ -464,6 +464,14 @@ class HookHandler(BaseHTTPRequestHandler):
       if field_tag in settable:
        attr = settable[field_tag]
        result["value"] = _serialize_for_api(_get_app_attr(app, attr, None))
+      elif "[" in field_tag and field_tag.endswith("]"):
+       dict_name, _, key_part = field_tag.partition("[")
+       key = key_part[:-1].strip().strip("'\"")
+       if dict_name in settable:
+        attr = settable[dict_name]
+        current = _get_app_attr(app, attr, None)
+        if isinstance(current, dict) and key in current:
+         result["value"] = _serialize_for_api(current[key])
      finally: event.set()
     lock = _get_app_attr(app, "_pending_gui_tasks_lock")
     tasks = _get_app_attr(app, "_pending_gui_tasks")