refactor: remove dead code — 1,784 lines across 77 files (#9180)

Deep scan with vulture, pyflakes, and manual cross-referencing identified:
- 41 dead functions/methods (zero callers in production)
- 7 production-dead functions (only test callers, tests deleted)
- 5 dead constants/variables
- ~35 unused imports across agent/, hermes_cli/, tools/, gateway/

Categories of dead code removed:
- Refactoring leftovers: _set_default_model, _setup_copilot_reasoning_selection,
  rebuild_lookups, clear_session_context, get_logs_dir, clear_session
- Unused API surface: search_models_dev, get_pricing, skills_categories,
  get_read_files_summary, clear_read_tracker, menu_labels, get_spinner_list
- Dead compatibility wrappers: schedule_cronjob, list_cronjobs, remove_cronjob
- Stale debug helpers: get_debug_session_info copies in 4 tool files
  (centralized version in debug_helpers.py already exists)
- Dead gateway methods: send_emote, send_notice (matrix), send_reaction
  (bluebubbles), _normalize_inbound_text (feishu), fetch_room_history
  (matrix), _start_typing_indicator (signal), parse_feishu_post_content
- Dead constants: NOUS_API_BASE_URL, SKILLS_TOOL_DESCRIPTION,
  FILE_TOOLS, VALID_ASPECT_RATIOS, MEMORY_DIR
- Unused UI code: _interactive_provider_selection,
  _interactive_model_selection (superseded by prompt_toolkit picker)

Test suite verified: 609 tests covering affected files all pass.
Tests for removed functions deleted. Tests using removed utilities
(clear_read_tracker, MEMORY_DIR) updated to use internal APIs directly.

tests/tools/test_file_tools.py

@@ -9,7 +9,6 @@ import logging
 from unittest.mock import MagicMock, patch
 
 from tools.file_tools import (
-    FILE_TOOLS,
     READ_FILE_SCHEMA,
     WRITE_FILE_SCHEMA,
     PATCH_SCHEMA,
@@ -17,23 +16,6 @@ from tools.file_tools import (
 )
 
 
-class TestFileToolsList:
-    def test_has_expected_entries(self):
-        names = {t["name"] for t in FILE_TOOLS}
-        assert names == {"read_file", "write_file", "patch", "search_files"}
-
-    def test_each_entry_has_callable_function(self):
-        for tool in FILE_TOOLS:
-            assert callable(tool["function"]), f"{tool['name']} missing callable"
-
-    def test_schemas_have_required_fields(self):
-        """All schemas must have name, description, and parameters with properties."""
-        for schema in [READ_FILE_SCHEMA, WRITE_FILE_SCHEMA, PATCH_SCHEMA, SEARCH_FILES_SCHEMA]:
-            assert "name" in schema
-            assert "description" in schema
-            assert "properties" in schema["parameters"]
-
-
 class TestReadFileHandler:
     @patch("tools.file_tools._get_file_ops")
     def test_returns_file_content(self, mock_get):
@@ -258,8 +240,8 @@ class TestSearchHints:
 
     def setup_method(self):
         """Clear read/search tracker between tests to avoid cross-test state."""
-        from tools.file_tools import clear_read_tracker
-        clear_read_tracker()
+        from tools.file_tools import _read_tracker
+        _read_tracker.clear()
 
     @patch("tools.file_tools._get_file_ops")
     def test_truncated_results_hint(self, mock_get):