feat: initial pi-review Docker action

Reusable Gitea/GitHub action that runs Pi coding agent for
AI-powered code reviews on pull requests.

- Docker image based on node:24-slim (112 packages)
- Supports built-in providers (zai, anthropic, openai, deepseek, openrouter)
  and custom OpenAI-compatible endpoints
- Generates git diff (excludes lockfiles/generated code by default)
- Posts review as idempotent PR comment (updates existing on re-run)
- Read-only tools only: agent investigates but never modifies code
- 80KB default diff truncation to stay within LLM context windows
- No curl/python3 dependency — uses Node.js for HTTP and JSON

package.json

@@ -0,0 +1,20 @@
+{
+  "name": "pi-review",
+  "version": "1.0.0",
+  "description": "",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "devEngines": {
+    "packageManager": {
+      "name": "pnpm",
+      "version": "^11.1.2",
+      "onFail": "download"
+    }
+  },
+  "type": "module"
+}