feat: Phase 1+2 — project setup and core infrastructure

- requirements.txt, config.yaml, .env, Dockerfile, docker-compose.yml
- app/core: config (YAML+env override), logging (JSON structured),
  exceptions (typed hierarchy), json_utils (Markdown fence stripping)
- app/clients: LLMClient ABC + ZhipuAIClient (run_in_executor),
  StorageClient ABC + RustFSClient (boto3 head_object for size check)
- app/main.py: FastAPI app with health endpoint and router registration
- app/core/dependencies.py: lru_cache singleton factories
- tests/conftest.py: mock_llm, mock_storage, test_app, client fixtures
- pytest.ini: asyncio_mode=auto
- 11 unit tests passing

tests/test_config.py

@@ -0,0 +1,40 @@
+import os
+import pytest
+
+
+def test_yaml_defaults_load(monkeypatch):
+    # Clear lru_cache so each test gets a fresh load
+    from app.core import config as cfg_module
+    cfg_module.get_config.cache_clear()
+
+    # Remove env overrides that might bleed from shell environment
+    for var in ["MAX_VIDEO_SIZE_MB", "LOG_LEVEL", "STORAGE_ENDPOINT"]:
+        monkeypatch.delenv(var, raising=False)
+
+    cfg = cfg_module.get_config()
+
+    assert cfg["server"]["port"] == 8000
+    assert cfg["video"]["max_file_size_mb"] == 200
+    assert cfg["models"]["default_text"] == "glm-4-flash"
+    assert cfg["models"]["default_vision"] == "glm-4v-flash"
+    assert cfg["storage"]["buckets"]["source_data"] == "source-data"
+
+
+def test_max_video_size_env_override(monkeypatch):
+    from app.core import config as cfg_module
+    cfg_module.get_config.cache_clear()
+
+    monkeypatch.setenv("MAX_VIDEO_SIZE_MB", "500")
+    cfg = cfg_module.get_config()
+
+    assert cfg["video"]["max_file_size_mb"] == 500
+
+
+def test_log_level_env_override(monkeypatch):
+    from app.core import config as cfg_module
+    cfg_module.get_config.cache_clear()
+
+    monkeypatch.setenv("LOG_LEVEL", "DEBUG")
+    cfg = cfg_module.get_config()
+
+    assert cfg["server"]["log_level"] == "DEBUG"