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  _interactive_model_selection (superseded by prompt_toolkit picker)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.

hermes_cli/plugins.py

@@ -31,7 +31,6 @@ import importlib
 import importlib.metadata
 import importlib.util
 import logging
-import os
 import sys
 import types
 from dataclasses import dataclass, field
@@ -584,19 +583,6 @@ def invoke_hook(hook_name: str, **kwargs: Any) -> List[Any]:
     return get_plugin_manager().invoke_hook(hook_name, **kwargs)
 
 
-def get_plugin_tool_names() -> Set[str]:
-    """Return the set of tool names registered by plugins."""
-    return get_plugin_manager()._plugin_tool_names
-
-
-def get_plugin_cli_commands() -> Dict[str, dict]:
-    """Return CLI commands registered by general plugins.
-
-    Returns a dict of ``{name: {help, setup_fn, handler_fn, ...}}``
-    suitable for wiring into argparse subparsers.
-    """
-    return dict(get_plugin_manager()._cli_commands)
-
 
 def get_plugin_context_engine():
     """Return the plugin-registered context engine, or None."""