feat(studio): add MiniMax video generation

[octo-patch]

Reason: add target video capability using the existing tool and provider pattern

Summary

• Add a MiniMax text-to-video helper using the documented create, status, and file retrieval workflow.
• Default to the current text-to-video model, enforce bounded polling and request timeouts, and surface logical API errors.
• Expose a studio SSE endpoint that stores generated MP4 files in the existing project asset store.
• Add request-capture tests for the successful workflow and failed task handling.

Validation

• pnpm exec biome lint packages/core/src/minimax.ts packages/core/src/index.ts packages/core/test/minimax-video.test.ts
• pnpm --filter @html-video/core test
• pnpm --filter @html-video/cli... build
• pnpm --filter @html-video/cli test
• pnpm -r typecheck

Existing repository issue

• pnpm -r test reaches the runtime and core tests, then stops because @html-video/adapter-hyperframes runs node --test test/ but that package has no test/ directory.

[nettee]

This adds a MiniMax video-generation backend flow, but one blocking gap remains before it works as a Studio feature.

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[nettee]

At startStudioServer()'s new /api/projects/:id/generate-video branch, the server-side flow is implemented but nothing in the Studio client calls it yet. packages/project-studio/public/app.js still only posts to /generate-audio and only handles audio_* SSE events, and a repo-wide search shows no fetch to /generate-video or handling for video_started / video_done. That means the feature described by this PR is still unreachable for Studio users even though the backend route exists. Please either wire this endpoint and its SSE events into the Studio UI in the same PR, or explicitly scope the change down to a backend-only API and adjust the feature/tests accordingly.

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[octo-patch]

Thanks for the review. I wired the Studio client to /generate-video, added SSE handling for started/progress/done/failed events, and added an inline MP4 preview for generated assets. I pushed commit 12211e0. I ran Node syntax checks, project-studio typecheck, core TypeScript typecheck, and minimax-video.test.ts (2 passed).

[lefarcen]

Hey @octo-patch — catching up on the opened-path triage I missed earlier. Thanks for the PR, and thanks for pushing the 12211e0 follow-up with the Studio wiring; I’ve re-requested review on this updated head, and product review is also still in flight because this is now clearly a user-facing Studio feature.

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