POC scaffold: extension manifest + tooling config (Feature #2)

Manifest declares the cowriting.showClineSdkInfo command; esbuild + vitest +
tsc tooling. @cline/sdk@0.0.46 as a runtime dependency. Per issue #2 (epic #1).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tsconfig.json

@@ -0,0 +1,15 @@
+{
+  "compilerOptions": {
+    "module": "ESNext",
+    "moduleResolution": "Bundler",
+    "target": "ES2022",
+    "lib": ["ES2022"],
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "resolveJsonModule": true,
+    "noEmit": true,
+    "types": ["node"]
+  },
+  "include": ["src", "test", "esbuild.mjs"]
+}