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  _interactive_model_selection (superseded by prompt_toolkit picker)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.

gateway/platforms/signal.py

@@ -17,7 +17,6 @@ import json
 import logging
 import os
 import random
-import re
 import time
 from datetime import datetime, timezone
 from pathlib import Path
@@ -781,21 +780,6 @@ class SignalAdapter(BasePlatformAdapter):
     # Typing Indicators
     # ------------------------------------------------------------------
 
-    async def _start_typing_indicator(self, chat_id: str) -> None:
-        """Start a typing indicator loop for a chat."""
-        if chat_id in self._typing_tasks:
-            return  # Already running
-
-        async def _typing_loop():
-            try:
-                while True:
-                    await self.send_typing(chat_id)
-                    await asyncio.sleep(TYPING_INTERVAL)
-            except asyncio.CancelledError:
-                pass
-
-        self._typing_tasks[chat_id] = asyncio.create_task(_typing_loop())
-
     async def _stop_typing_indicator(self, chat_id: str) -> None:
         """Stop a typing indicator loop for a chat."""
         task = self._typing_tasks.pop(chat_id, None)