feat: add Grok Imagine models and 1080p

[erickkkyt]

Summary

• add Grok Imagine Image 2.0 and Video 1.5 to Studio and Canvas composers
• send BeatAPI-compatible image/video requests, including 1080p and duration controls
• enforce Grok-specific reference, aspect-ratio, prompt, and 1080p single-image constraints
• add per-second Grok video pricing rows and reuse the Grok SVG icon

Validation

• pnpm test
• pnpm typecheck
• pnpm i18n:check
• pnpm build
• Grok icon mapping regression test
• security scan clean

Not run

• paid provider generation E2E
• Cloudflare deployment (GitHub publish only, per request)