fix(feature-flags): bare flags default to true, robust coercion, drop wrapper

Address code review feedback:
- _coerce_flag_value: wrap coercion in try/except (ValueError, TypeError)
  and log a warning instead of crashing startup on malformed values.
- _parse_cli_feature_flags: bare --feature-flag KEY (no '=') now defaults
  to 'true' so registered bool flags work as toggles.
- Remove the get_cli_feature_flag_registry() wrapper; export and use
  CLI_FEATURE_FLAG_REGISTRY directly in main.py and tests.

Add tests for coercion-failure fallback and bare-flag default behavior.

Co-authored-by: Amp <amp@ampcode.com>
Amp-Thread-ID: https://ampcode.com/threads/T-019deba2-bfe2-7118-913c-562beee48972

main.py

@@ -5,8 +5,8 @@ from comfy.cli_args import args
 
 if args.list_feature_flags:
     import json
-    from comfy_api.feature_flags import get_cli_feature_flag_registry
-    print(json.dumps(get_cli_feature_flag_registry(), indent=2))  # noqa: T201
+    from comfy_api.feature_flags import CLI_FEATURE_FLAG_REGISTRY
+    print(json.dumps(CLI_FEATURE_FLAG_REGISTRY, indent=2))  # noqa: T201
     raise SystemExit(0)
 
 import os