fix(mcp): clarify enabledTools filtering semantics

- support both raw and wrapped MCP tool names
- treat [\"*\"] as all tools and [] as no tools
- add warnings, tests, and README docs for enabledTools

nanobot/config/schema.py

@@ -140,7 +140,7 @@ class MCPServerConfig(Base):
     url: str = ""  # HTTP/SSE: endpoint URL
     headers: dict[str, str] = Field(default_factory=dict)  # HTTP/SSE: custom headers
     tool_timeout: int = 30  # seconds before a tool call is cancelled
-    enabled_tools: list[str] = Field(default_factory=list)  # Only register these tools; empty = all tools
+    enabled_tools: list[str] = Field(default_factory=lambda: ["*"])  # Only register these tools; accepts raw MCP names or wrapped mcp_<server>_<tool> names; ["*"] = all tools; [] = no tools
 
 class ToolsConfig(Base):
     """Tools configuration."""