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/roles.py

@@ -0,0 +1,22 @@
+import os
+import yaml
+
+ROLES_DIR = "/action/app/prompts/roles"
+
+
+def load_roles() -> list[dict]:
+    """載入所有角色定義"""
+    roles = []
+    for fname in sorted(os.listdir(ROLES_DIR)):
+        if fname.endswith(".yaml"):
+            with open(os.path.join(ROLES_DIR, fname), "r", encoding="utf-8") as f:
+                roles.append(yaml.safe_load(f))
+    return roles
+
+
+def get_role_intro(roles: list[dict]) -> str:
+    """產生角色介紹文字（用於 comment）"""
+    lines = ["## 🤖 AI Code Review 團隊", ""]
+    for r in roles:
+        lines.append(f"- **{r['name']}** ({r['role']}): {r['personality']}")
+    return "\n".join(lines)