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/mcp_tool.py

@@ -792,7 +792,7 @@ class MCPServerTask:
         After the initial ``await`` (list_tools), all mutations are synchronous
         — atomic from the event loop's perspective.
         """
-        from tools.registry import registry
+        from tools.registry import registry, tool_error
         from toolsets import TOOLSETS
 
         async with self._refresh_lock:
@@ -1326,7 +1326,7 @@ def _make_read_resource_handler(server_name: str, tool_timeout: float):
 
         uri = args.get("uri")
         if not uri:
-            return json.dumps({"error": "Missing required parameter 'uri'"})
+            return tool_error("Missing required parameter 'uri'")
 
         async def _call():
             result = await server.session.read_resource(uri)
@@ -1415,7 +1415,7 @@ def _make_get_prompt_handler(server_name: str, tool_timeout: float):
 
         name = args.get("name")
         if not name:
-            return json.dumps({"error": "Missing required parameter 'name'"})
+            return tool_error("Missing required parameter 'name'")
         arguments = args.get("arguments", {})
 
         async def _call():
@@ -1724,7 +1724,7 @@ def _register_server_tools(name: str, server: MCPServerTask, config: dict) -> Li
     Returns:
         List of registered prefixed tool names.
     """
-    from tools.registry import registry
+    from tools.registry import registry, tool_error
     from toolsets import create_custom_toolset, TOOLSETS
 
     registered_names: List[str] = []