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>

package.json

@@ -0,0 +1,42 @@
+{
+  "name": "vscode-cowriting-plugin",
+  "displayName": "Cowriting (Cline SDK POC)",
+  "description": "Non-shippable POC: a standalone VS Code extension that drives @cline/sdk.",
+  "version": "0.0.1",
+  "private": true,
+  "license": "Apache-2.0",
+  "publisher": "benstull",
+  "engines": {
+    "vscode": "^1.90.0",
+    "node": ">=22"
+  },
+  "categories": ["Other"],
+  "main": "./out/extension.cjs",
+  "activationEvents": [],
+  "contributes": {
+    "commands": [
+      {
+        "command": "cowriting.showClineSdkInfo",
+        "title": "Cowriting: Show Cline SDK Info",
+        "category": "Cowriting"
+      }
+    ]
+  },
+  "scripts": {
+    "build": "node esbuild.mjs",
+    "watch": "node esbuild.mjs --watch",
+    "typecheck": "tsc --noEmit",
+    "test": "vitest run",
+    "vscode:prepublish": "node esbuild.mjs"
+  },
+  "dependencies": {
+    "@cline/sdk": "0.0.46"
+  },
+  "devDependencies": {
+    "@types/node": "^22.0.0",
+    "@types/vscode": "^1.90.0",
+    "esbuild": "^0.23.0",
+    "typescript": "^5.5.0",
+    "vitest": "^2.0.0"
+  }
+}