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  _interactive_model_selection (superseded by prompt_toolkit picker)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.

agent/usage_pricing.py

@@ -575,25 +575,6 @@ def has_known_pricing(
     return entry is not None
 
 
-def get_pricing(
-    model_name: str,
-    provider: Optional[str] = None,
-    base_url: Optional[str] = None,
-    api_key: Optional[str] = None,
-) -> Dict[str, float]:
-    """Backward-compatible thin wrapper for legacy callers.
-
-    Returns only non-cache input/output fields when a pricing entry exists.
-    Unknown routes return zeroes.
-    """
-    entry = get_pricing_entry(model_name, provider=provider, base_url=base_url, api_key=api_key)
-    if not entry:
-        return {"input": 0.0, "output": 0.0}
-    return {
-        "input": float(entry.input_cost_per_million or _ZERO),
-        "output": float(entry.output_cost_per_million or _ZERO),
-    }
-
 
 def format_duration_compact(seconds: float) -> str:
     if seconds < 60: