simplify: unify 405 handlers, fix double-read in renameRundown, guard mcpClientConfig

- mcp.router.ts: extract identical GET/DELETE 405 responses into methodNotAllowed
- mcp.service.ts: pass the already-patched rundown object to initRundown instead
  of re-fetching it from the data provider
- McpSection.tsx: compute mcpClientConfig only when mcpEndpointUrl is truthy

https://claude.ai/code/session_01U24MeuUacYXeQhbX3tatEe

apps/client/src/features/app-settings/panel/feature-panel/McpSection.tsx

@@ -25,7 +25,9 @@ export default function McpSection() {
       });
   }, [infoData]);
 
-  const mcpClientConfig = JSON.stringify({ mcpServers: { ontime: { url: mcpEndpointUrl } } }, null, 2);
+  const mcpClientConfig = mcpEndpointUrl
+    ? JSON.stringify({ mcpServers: { ontime: { url: mcpEndpointUrl } } }, null, 2)
+    : '';
 
   return (
     <Panel.Section>