fix(build): add webpack IgnorePlugin for thread-stream test files; exclude compiled app/ dir from git

- thread-stream test fixtures (intentionally malformed) were being picked
  up by Turbopack during production build, causing 111 compile errors
- IgnorePlugin excludes /test/ within thread-stream context
- thread-stream added to serverExternalPackages to prevent bundling
- /app removed: it is a stale npm-package prebuild artifact, not source code

.gitignore

@@ -131,3 +131,6 @@ vscode-extension/
 *.sqlite-shm
 *.sqlite-wal
 *.sqlite-journal
+
+# Compiled npm-package build artifact (not source, should not be in git)
+/app

next.config.mjs

@@ -13,6 +13,7 @@ const nextConfig = {
   },
   output: "standalone",
   serverExternalPackages: [
+    "thread-stream",
     "better-sqlite3",
     "zod",
     "child_process",
@@ -37,8 +38,16 @@ const nextConfig = {
   images: {
     unoptimized: true,
   },
-  webpack: (config, { isServer }) => {
+  webpack: (config, { isServer, webpack }) => {
     if (isServer) {
+      // Webpack IgnorePlugin: skip thread-stream test files that contain
+      // intentionally broken syntax/imports (they cause Turbopack build errors)
+      config.plugins.push(
+        new webpack.IgnorePlugin({
+          resourceRegExp: /\/test\//,
+          contextRegExp: /thread-stream/,
+        })
+      );
       // ── Turbopack / Next.js 16 module-hash patch (#394, #396, #398) ────────
       //
       // Next.js 16 (with or without Turbopack) compiles the instrumentation hook