feat: 階段一 - 基本流程串接骨架

- 重寫 action.yaml：支援所有 LLM providers 的 inputs
- 重寫 Dockerfile：python:3.11-slim + git
- 重寫 entrypoint.sh：啟動 app/main.py
- app/config.py：環境變數與 LLM 自動偵測
- app/llm.py：OpenAI-compatible 統一介面
- app/gitea.py：PR diff 取得與 comment 發布
- app/roles.py：從 prompts/roles/*.yaml 載入角色
- app/main.py：pipeline 骨架，log 每個主要階段
- app/prompts/roles/：五個角色定義（Aria/Rex/Zara/Leo/Maya）

app/gitea.py

@@ -0,0 +1,26 @@
+import requests
+from config import GITEA_TOKEN, GITEA_SERVER_URL, GITEA_REPOSITORY, PR_NUMBER
+
+
+def _headers():
+    return {"Authorization": f"token {GITEA_TOKEN}", "Content-Type": "application/json"}
+
+
+def _api(path: str) -> str:
+    return f"{GITEA_SERVER_URL.rstrip('/')}/api/v1{path}"
+
+
+def get_pr_diff() -> str:
+    """取得 PR 的 git diff 內容"""
+    url = _api(f"/repos/{GITEA_REPOSITORY}/pulls/{PR_NUMBER}.diff")
+    resp = requests.get(url, headers=_headers(), timeout=60)
+    resp.raise_for_status()
+    return resp.text
+
+
+def post_comment(body: str) -> dict:
+    """在 PR 發布 comment"""
+    url = _api(f"/repos/{GITEA_REPOSITORY}/issues/{PR_NUMBER}/comments")
+    resp = requests.post(url, headers=_headers(), json={"body": body}, timeout=30)
+    resp.raise_for_status()
+    return resp.json()