refactor(c901): tools_search.py below C901 threshold (#1665)

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

Migrates the 5 closure-nested functions inside `register_search_tools`
to a `SearchTools` class, then decomposes the four over-threshold
methods into focused helpers:

- `_ha_search_entities` (80→<10): 4 branch helpers
  (`_search_area_with_query`, `_search_area_only`,
  `_search_area_only_populated`, `_search_domain_only`, `_search_regular`)
- `ha_get_state` (24→<10): `_get_single_entity_state`,
  `_get_bulk_entity_states`, `_accumulate_state_results`
- `ha_get_overview` (19→<10): `_fetch_system_info`,
  `_fetch_notifications`, `_fetch_repairs`
- `ha_search` (13→<10): `_apply_search_outcome` extracted
- `_exact_match_search` (13→<10): `_build_hidden_ids` extracted
- `_merge_payload_metadata` (12→<10): `_merge_list_key`,
  `_merge_partial_reason` extracted

Removes `tools_search.py` from the C901 per-file ignore in
`pyproject.toml` (3 files remain: dashboards, entities, registry).

* fix: resolve CodeQL findings and expand AST harvest coverage

- Remove redundant search_type assignment in _search_regular (py/multiple-definition)
- Add return None after raise_tool_error in _ha_search_entities except-ValueError block (py/mixed-returns)
- Add return None after exception_to_structured_error in _get_single_entity_state (py/mixed-returns)
- Expand test_entities_branch_emissions to scan _exact_match_search and _normalize_regular_search_result for complete key coverage

---------

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

Author: sergeykad

pyproject.toml

@@ -152,7 +152,6 @@ ignore = [
 "src/ha_mcp/tools/tools_config_dashboards.py" = ["C901"]
 "src/ha_mcp/tools/tools_entities.py" = ["C901"]
 "src/ha_mcp/tools/tools_registry.py" = ["C901"]
-"src/ha_mcp/tools/tools_search.py" = ["C901"]
 
 [tool.pytest.ini_options]
 testpaths = ["tests"]