refactor(c901): tools_entities.py below C901 threshold (#1692)

* refactor(c901): tools_entities.py below C901 threshold

- Convert closure pattern to EntityTools class; register_entity_tools
  becomes a 1-liner calling register_tool_methods(mcp, EntityTools(client))
- Extract 10 module-level pure helpers and 9 async class methods so all
  functions stay below McCabe complexity 10
- Remove "src/ha_mcp/tools/tools_entities.py" = ["C901"] exemption from
  pyproject.toml
- Fix bulk categories bug: old code hardcoded None for categories in
  gather; new code passes parsed_categories matching docstring and validation
- Fix updates_applied in Phase-4 error context: expose_to= and device_name
  entries are now appended after their WS phases run, not pre-appended
- Unify _parse_aliases_param/_parse_labels_param into _parse_string_list_field
- Flatten double-nested if in _validate_enabled_constraint
- Update test fixtures from mcp.tool capture to mcp.add_tool capture
- Add test_bulk_categories_set regression test

* fix: address Gemini review on PR #1692

- Guard all result.get("result", {}) calls with `or {}` so a null
  "result" key from HA never produces an AttributeError on .get()
- Change expose_to entity-entry fetch guard from has_registry_updates
  to `not entity_entry` — avoids redundant WS round-trip when options
  or device_rename already populated entity_entry

---------

Co-authored-by: Sergey <sergey@example.com>

Author: sergeykad

pyproject.toml

@@ -150,7 +150,6 @@ ignore = [
 # C901 ignores for tools files with complex methods (see #925).
 # Remove lines as individual methods are simplified below threshold.
 "src/ha_mcp/tools/tools_config_dashboards.py" = ["C901"]
-"src/ha_mcp/tools/tools_entities.py" = ["C901"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]