refactor: introduce mcpcore and clean up STDIO transport

- Extract core MCP logic into a new `mcpcore` module
- Remove logging that interferes with JSON-RPC over STDIO
- Improve server loop to parse requests before handling
- Add stub for `logging/setLevel` JSON-RPC method
- Refactor vcode server into a dedicated logic submodule

lib/ai/mcp/vcode/write_vfile_tool.v

@@ -0,0 +1,72 @@
+module vcode
+
+// import freeflowuniverse.herolib.ai.mcpcore
+// TODO: Uncomment when mcpcore module is fixed
+/*
+// import freeflowuniverse.herolib.develop.codetools as code
+import freeflowuniverse.herolib.schemas.jsonschema
+import x.json2 { Any }
+
+const write_vfile_tool = mcpcore.Tool{
+	name:         'write_vfile'
+	description:  'write_vfile parses a V code string into a VFile and writes it to the specified path
+ARGS:
+path string - directory path where to write the file
+code string - V code content to write
+format bool - whether to format the code (optional, default: false)
+overwrite bool - whether to overwrite existing file (optional, default: false)
+prefix string - prefix to add to the filename (optional, default: "")
+RETURNS: string - success message with the path of the written file'
+	input_schema: jsonschema.Schema{
+		typ:        'object'
+		properties: {
+			'path':      jsonschema.SchemaRef(jsonschema.Schema{
+				typ: 'string'
+			})
+			'code':      jsonschema.SchemaRef(jsonschema.Schema{
+				typ: 'string'
+			})
+			'format':    jsonschema.SchemaRef(jsonschema.Schema{
+				typ: 'boolean'
+			})
+			'overwrite': jsonschema.SchemaRef(jsonschema.Schema{
+				typ: 'boolean'
+			})
+			'prefix':    jsonschema.SchemaRef(jsonschema.Schema{
+				typ: 'string'
+			})
+		}
+		required:   ['path', 'code']
+	}
+}
+*/
+
+// TODO: Uncomment when mcpcore module is fixed
+/*
+pub fn (d &VCode) write_vfile_tool_handler(arguments map[string]Any) !mcpcore.ToolCallResult {
+	path := arguments['path'] or {
+		return mcpcore.error_tool_call_result(error('Missing path argument'))
+	}.str()
+	code_str := arguments['code'] or {
+		return mcpcore.error_tool_call_result(error('Missing code argument'))
+	}.str()
+
+	// Parse optional parameters with defaults
+	format := if 'format' in arguments { arguments['format'] or { false }.bool() } else { false }
+	overwrite := if 'overwrite' in arguments {
+		arguments['overwrite'] or { false }.bool()
+	} else {
+		false
+	}
+	prefix := if 'prefix' in arguments { arguments['prefix'] or { '' }.str() } else { '' }
+
+	// TODO: Implement actual V file parsing and writing
+	// For now, return a placeholder message
+	result := 'Writing V file to ${path} with code length ${code_str.len} (format: ${format}, overwrite: ${overwrite}, prefix: "${prefix}") is not yet implemented'
+
+	return mcpcore.ToolCallResult{
+		is_error: false
+		content:  mcpcore.result_to_mcp_tool_contents[string](result)
+	}
+}
+*/