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  _interactive_model_selection (superseded by prompt_toolkit picker)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/feishu.py

@@ -430,14 +430,6 @@ def _build_markdown_post_payload(content: str) -> str:
     )
 
 
-def parse_feishu_post_content(raw_content: str) -> FeishuPostParseResult:
-    try:
-        parsed = json.loads(raw_content) if raw_content else {}
-    except json.JSONDecodeError:
-        return FeishuPostParseResult(text_content=FALLBACK_POST_TEXT)
-    return parse_feishu_post_payload(parsed)
-
-
 def parse_feishu_post_payload(payload: Any) -> FeishuPostParseResult:
     resolved = _resolve_post_payload(payload)
     if not resolved:
@@ -2688,12 +2680,6 @@ class FeishuAdapter(BasePlatformAdapter):
             return self._resolve_media_message_type(media_types[0] if media_types else "", default=MessageType.DOCUMENT)
         return MessageType.TEXT
 
-    def _normalize_inbound_text(self, text: str) -> str:
-        """Strip Feishu mention placeholders from inbound text."""
-        text = _MENTION_RE.sub(" ", text or "")
-        text = _MULTISPACE_RE.sub(" ", text)
-        return text.strip()
-
     async def _maybe_extract_text_document(self, cached_path: str, media_type: str) -> str:
         if not cached_path or not media_type.startswith("text/"):
             return ""