refactor: add tool_error/tool_result helpers + read_raw_config, migrate 129 callsites

Add three reusable helpers to eliminate pervasive boilerplate:

tools/registry.py — tool_error() and tool_result():
  Every tool handler returns JSON strings. The pattern
  json.dumps({"error": msg}, ensure_ascii=False) appeared 106 times,
  and json.dumps({"success": False, "error": msg}, ...) another 23.
  Now: tool_error(msg) or tool_error(msg, success=False).

  tool_result() handles arbitrary result dicts:
  tool_result(success=True, data=payload) or tool_result(some_dict).

hermes_cli/config.py — read_raw_config():
  Lightweight YAML reader that returns the raw config dict without
  load_config()'s deep-merge + migration overhead. Available for
  callsites that just need a single config value.

Migration (129 callsites across 32 files):
- tools/: browser_camofox (18), file_tools (10), homeassistant (8),
  web_tools (7), skill_manager (7), cronjob (11), code_execution (4),
  delegate (5), send_message (4), tts (4), memory (7), session_search (3),
  mcp (2), clarify (2), skills_tool (3), todo (1), vision (1),
  browser (1), process_registry (2), image_gen (1)
- plugins/memory/: honcho (9), supermemory (9), hindsight (8),
  holographic (7), openviking (7), mem0 (7), byterover (6), retaindb (2)
- agent/: memory_manager (2), builtin_memory_provider (1)

tools/session_search_tool.py

@@ -241,7 +241,7 @@ def _list_recent_sessions(db, limit: int, current_session_id: str = None) -> str
         }, ensure_ascii=False)
     except Exception as e:
         logging.error("Error listing recent sessions: %s", e, exc_info=True)
-        return json.dumps({"success": False, "error": f"Failed to list recent sessions: {e}"}, ensure_ascii=False)
+        return tool_error(f"Failed to list recent sessions: {e}", success=False)
 
 
 def session_search(
@@ -258,7 +258,7 @@ def session_search(
     The current session is excluded from results since the agent already has that context.
     """
     if db is None:
-        return json.dumps({"success": False, "error": "Session database not available."}, ensure_ascii=False)
+        return tool_error("Session database not available.", success=False)
 
     limit = min(limit, 5)  # Cap at 5 sessions to avoid excessive LLM calls
 
@@ -427,7 +427,7 @@ def session_search(
 
     except Exception as e:
         logging.error("Session search failed: %s", e, exc_info=True)
-        return json.dumps({"success": False, "error": f"Search failed: {str(e)}"}, ensure_ascii=False)
+        return tool_error(f"Search failed: {str(e)}", success=False)
 
 
 def check_session_search_requirements() -> bool:
@@ -487,7 +487,7 @@ SESSION_SEARCH_SCHEMA = {
 
 
 # --- Registry ---
-from tools.registry import registry
+from tools.registry import registry, tool_error
 
 registry.register(
     name="session_search",