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/test_config.py

@@ -0,0 +1,57 @@
+"""Unit tests for config.py pure functions."""
+
+import sys
+from pathlib import Path
+
+import pytest
+
+sys.path.insert(0, str(Path(__file__).parent.parent / "skills" / "ir_generation_skill"))
+import config
+
+
+def test_set_input_file():
+    original = config.INPUT_JSON
+    try:
+        config.set_input_file("/tmp/test_input.json")
+        assert config.INPUT_JSON == "/tmp/test_input.json"
+    finally:
+        config.set_input_file(original)
+
+
+def test_config_constants_exist():
+    """Verify all expected path constants are defined."""
+    assert config.BASE_DIR
+    assert config.OUTPUT_DIR
+    assert config.PROMPTS_DIR
+    assert config.TESTS_DIR
+    assert config.DOC_PARSER_OUTPUT
+    assert config.SEMANTIC_INDEX_JSON
+    assert config.IR_FRAGMENTS_JSON
+    assert config.PATH_ENUM_JSON
+    assert config.IR_AUTOCOMPLETE_FRAGMENTS_JSON
+    assert config.IR_FINAL_JSON
+    assert config.IR_AUDIT_REPORT_MD
+
+
+def test_ensemble_temperatures_count():
+    """Should have exactly 3 ensemble temperatures."""
+    assert len(config.ENSEMBLE_TEMPERATURES) == 3
+
+
+def test_max_tokens_is_int():
+    assert isinstance(config.MAX_TOKENS, int)
+    assert config.MAX_TOKENS > 0
+
+
+def test_temperature_is_float():
+    assert isinstance(config.TEMPERATURE, float)
+    assert 0.0 <= config.TEMPERATURE <= 2.0
+
+
+def test_provider_models_has_expected_keys():
+    assert "deepseek" in config.PROVIDER_MODELS
+    assert "dashscope" in config.PROVIDER_MODELS
+
+
+def test_model_name_in_provider_models():
+    assert config.MODEL_NAME in config.PROVIDER_MODELS.values()