Add unified generation and Effect commands

[erickkkyt]

What changed

• add typed client methods for model discovery, image/video generation, and Effects
• add CLI commands for models, images, videos, and Effect discovery/task creation
• regenerate TypeScript types from the final OpenAPI contract
• refresh package documentation, changelog, and README visuals
• lock the contract to beatapi-examples commit 5fbea4d

Validation

• contract hash and generated types checks passed
• TypeScript typecheck passed
• 26 tests passed
• package build, dry-run pack, and installed-package smoke tests passed
• OpenAPI TypeScript generation completed with zero warnings
• secret-pattern and credential-handling review passed