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/send_message_tool.py

@@ -101,7 +101,7 @@ def _handle_send(args):
     target = args.get("target", "")
     message = args.get("message", "")
     if not target or not message:
-        return json.dumps({"error": "Both 'target' and 'message' are required when action='send'"})
+        return tool_error("Both 'target' and 'message' are required when action='send'")
 
     parts = target.split(":", 1)
     platform_name = parts[0].strip().lower()
@@ -134,7 +134,7 @@ def _handle_send(args):
 
     from tools.interrupt import is_interrupted
     if is_interrupted():
-        return json.dumps({"error": "Interrupted"})
+        return tool_error("Interrupted")
 
     try:
         from gateway.config import load_gateway_config, Platform
@@ -160,11 +160,11 @@ def _handle_send(args):
     platform = platform_map.get(platform_name)
     if not platform:
         avail = ", ".join(platform_map.keys())
-        return json.dumps({"error": f"Unknown platform: {platform_name}. Available: {avail}"})
+        return tool_error(f"Unknown platform: {platform_name}. Available: {avail}")
 
     pconfig = config.platforms.get(platform)
     if not pconfig or not pconfig.enabled:
-        return json.dumps({"error": f"Platform '{platform_name}' is not configured. Set up credentials in ~/.hermes/config.yaml or environment variables."})
+        return tool_error(f"Platform '{platform_name}' is not configured. Set up credentials in ~/.hermes/config.yaml or environment variables.")
 
     from gateway.platforms.base import BasePlatformAdapter
 
@@ -940,7 +940,7 @@ def _check_send_message():
 
 
 # --- Registry ---
-from tools.registry import registry
+from tools.registry import registry, tool_error
 
 registry.register(
     name="send_message",