fix: 完善 UT 覆盖，统一 pytest 测试发现 - Closes #2

- 新建 pytest.ini 统一 test discovery（tests/ + skills/ir_generation_skill/tests/）
- test_step1~3 转换为 pytest 兼容格式，无输出文件时自动 skip
- 新增 tests/test_detect_conflicts.py（18 个纯函数单测）
- 新增 tests/test_config.py（7 个配置模块单测）
- CI 改为 pytest -v 使用 pytest.ini testpaths
- DEV_AGENT.md 新增 PR 提交规范

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/acceptance/conftest.py

@@ -258,21 +258,27 @@ def acceptance_runs(request) -> int:
 def run_ir_pipeline():
     """Return a callable that runs the IR generation pipeline on a parsed JSON.
 
+    Returns None if the pipeline script is not available in the current environment.
+    This is common when the acceptance tests run on pre-generated IR output.
+
     Usage::
 
-        ir_data, ir_path = run_ir_pipeline(parsed_json_path, output_dir)
+        runner = run_ir_pipeline()
+        if runner:
+            ir_data, ir_path = runner(parsed_json_path, output_dir)
     """
-    sys.path.insert(0, _skill_path("ir_generation_skill"))
+    ir_gen_path = (
+        _PROJECT_ROOT / "skills" / "ir_generation_skill" / "scripts" / "ir_generator.py"
+    )
+    if not ir_gen_path.exists():
+        return None
+
+    sys.path.insert(0, str(ir_gen_path.parent))
     from ir_generator import generate_ir
 
-    def _run(parsed_path: str, output_dir: str | None = None) -> tuple[dict, str]:
-        """Run IR generation and return (ir_data, ir_path)."""
+    def _run(parsed_path: str, output_dir: str | None = None) -> tuple[list, str]:
         out = output_dir or tempfile.mkdtemp(prefix="qe_acceptance_")
         result = generate_ir(parsed_path, out, dry_run=False)
-        ir_list = result.get("ir", [])
-        ir_path = result.get("path", "")
-        # ir_generator produces a list; wrap to match rich format expectations
-        # for schema validation we accept both formats
-        return ir_list, ir_path
+        return result.get("ir", []), result.get("path", "")
 
     return _run