Video generation through the managed Nous gateway (PR #33259) shipped
without docs. Add it everywhere the other gateway tools are documented:
- nous-portal.md: gateway tools table (now six backends), config ref
- tool-gateway.md: capabilities table, 'Using individual video models'
section with model short-names + the gateway-allowlist 4xx caveat,
use_gateway config example, frontmatter/intro
- tools-reference.md: video_gen backends list + Nous Subscription path
- providers.md: video gen row in Optional API Keys
Note video_gen uses provider: fal + use_gateway: true (the FAL plugin
routes through the gateway), unlike image_gen's provider: nous.
bc29596b6c