fix(mcp): bundle build with esbuild so plugin cache never needs node_modules

Claude Code spawns plugin MCP servers straight from the read-only
git-content plugin cache, which never gets an npm install for mcp/. The
old tsc-multi-file build imported bare specifiers that only resolved
via mcp/node_modules, so every fresh plugin install/update produced a
-32000 reconnect failure. Bundle mcp/src into a single dependency-free
build/index.js instead; the one CJS-heavy import (express, only used
by --transport=http) is now dynamic so the stdio path never evaluates it.

mcp/package.json

@@ -10,7 +10,7 @@
   "scripts": {
     "clean": "node -e \"require('node:fs').rmSync('build',{recursive:true,force:true})\"",
     "typecheck": "tsc -p tsconfig.json --noEmit",
-    "build": "npm run clean && tsc -p tsconfig.json",
+    "build": "npm run clean && npm run typecheck && esbuild src/index.ts --bundle --platform=node --format=esm --target=node18 --outfile=build/index.js",
     "start": "node build/index.js",
     "start:http": "node build/index.js --transport=http",
     "start:repl": "node build/index.js --transport=repl",
@@ -29,6 +29,7 @@
   "devDependencies": {
     "@types/express": "^5.0.6",
     "@types/node": "^22.18.0",
+    "esbuild": "^0.24.0",
     "tsx": "^4.20.5",
     "typescript": "^5.9.2"
   },