feat(video_gen): wire Nous subscription override into hermes tools UX

Add the same managed-gateway UX that image_gen already has:

- TOOL_CATEGORIES['video_gen'] gets a 'Nous Subscription' provider row
  with managed_nous_feature='video_gen' + video_gen_plugin_name='fal'
- NousSubscriptionFeatures gains a video_gen property + feature state
  computation (managed/active/available using the fal-queue gateway)
- _GATEWAY_TOOL_LABELS, _GATEWAY_DIRECT_LABELS, _ALL_GATEWAY_KEYS,
  _get_gateway_direct_credentials, opted_in all include video_gen
- apply_nous_managed_defaults and apply_gateway_defaults handle video_gen
- _is_toolset_satisfied checks Nous features for video_gen
- _is_provider_active detects managed video_gen (use_gateway + fal provider)
- _select_plugin_video_gen_provider accepts use_gateway kwarg, propagated
  from all 4 call sites in _configure_provider when managed_feature is set
- hermes setup status shows 'Video Generation (FAL via Nous subscription)'

Users on a Nous subscription can now pick 'Nous Subscription' under
hermes tools → Video Generation, which sets video_gen.provider=fal +
video_gen.use_gateway=true. The FAL plugin's _resolve_managed_fal_video_gateway
then routes through the managed queue gateway — no FAL_KEY needed.

tests/hermes_cli/test_setup_model_provider.py

@@ -498,6 +498,7 @@ def test_setup_summary_shows_camofox_when_browser_feature_is_camofox(tmp_path, m
             features={
                 "web": NousFeatureState("web", "Web tools", True, False, False, False, False, True, ""),
                 "image_gen": NousFeatureState("image_gen", "Image generation", True, False, False, False, False, True, ""),
+                "video_gen": NousFeatureState("video_gen", "Video generation", False, False, False, False, False, False, ""),
                 "tts": NousFeatureState("tts", "OpenAI TTS", True, False, False, False, False, True, ""),
                 "browser": NousFeatureState("browser", "Browser automation", True, True, True, False, True, True, "Camofox"),
                 "modal": NousFeatureState("modal", "Modal execution", False, False, False, False, False, True, "local"),
@@ -525,6 +526,7 @@ def test_setup_summary_does_not_mark_incomplete_browserbase_as_available(tmp_pat
             features={
                 "web": NousFeatureState("web", "Web tools", True, False, False, False, False, True, ""),
                 "image_gen": NousFeatureState("image_gen", "Image generation", True, False, False, False, False, True, ""),
+                "video_gen": NousFeatureState("video_gen", "Video generation", False, False, False, False, False, False, ""),
                 "tts": NousFeatureState("tts", "OpenAI TTS", True, False, False, False, False, True, ""),
                 "browser": NousFeatureState("browser", "Browser automation", True, False, False, False, False, True, "Browserbase"),
                 "modal": NousFeatureState("modal", "Modal execution", False, False, False, False, False, True, "local"),