Parse config.yaml into typed AppConfig dataclass

- ServerConfig, VideoConfig, ModelConfig, DeadBugConfig,
  AudioConfig, LoggingConfig as nested dataclasses
- Consumers use config.server.host, config.model.resolved_path etc.
- env var overrides preserved via _apply_env_overrides()

app/core/lifecycle.py

@@ -1,10 +1,10 @@
 from __future__ import annotations
 
 from app.diagnostics.crash_handler import enable_crash_handler
-from configs.load import LOG_DIR
+from configs.load import config
 
 
 def startup() -> None:
-    enable_crash_handler(LOG_DIR)
+    enable_crash_handler(config.logging.dir_path)
     from app.core.logging import setup_logging
     setup_logging()