feat(video): add MuAPI provider

[Anil-matcha]

Summary

• add MuAPI as a first-class BYO video provider
• submit and poll MuAPI generation jobs, then validate and save the returned MP4
• support text-to-video and an optional first-frame image-to-video request
• support MUAPI_API_KEY, endpoint/model overrides, and the existing CLI/MCP video surfaces

Configuration

Set video.provider to "muapi" and provide MUAPI_API_KEY (or use the existing
OVS_VIDEO_* overrides). The default endpoint is https://api.muapi.ai/api/v1; text-to-video
defaults to kling-v2.1-master-t2v, and a first-frame image defaults to
kling-v2.1-standard-i2v. See the MuAPI API reference
for the submit-and-poll API contract.

The adapter intentionally exposes the common prompt, aspect-ratio, duration, and first-frame
inputs. Model-specific resolution, audio, edit, and additional-reference controls are rejected
clearly instead of being silently ignored.

Verification

• corepack pnpm vitest run packages/tools/test/gen.test.ts (25 passed)
• corepack pnpm build
• corepack pnpm typecheck
• corepack pnpm test (245 passed, 10 skipped)
• corepack pnpm test:video (26 passed)
• git diff --check

No live provider request or credentials are included in the change.