fix(producer): keep video captures viewport-bound on software

[miguel-heygen]

What

Fixes #1715 by stopping video compositions from forcing Chrome's beyond-viewport screenshot compositor under software rendering.

Why

The latest #1715 analysis checks out at source level: both the in-process renderer and distributed chunk renderer forced captureBeyondViewport: true whenever a composition had native videos. That preserves a hardware-rendering workaround, but on SwiftShader/software render hosts it sends every frame through a much more expensive full-surface compositor path. Distributed chunks are explicitly software-only, so they were always taking the slow path for video compositions.

How

• Added resolveVideoCaptureBeyondViewport(videoCount, browserGpuMode) so the video workaround is only enabled on resolved hardware rendering.
• In the in-process renderer, resolve the actual browser GPU mode via the engine's cached resolveBrowserGpuMode(...) before building capture options. auto therefore uses the real probed hardware/software result, not the requested string.
• In distributed chunks, pass the known software mode and explicitly set captureBeyondViewport: false for video chunks.
• Leave no-video renders unchanged by returning undefined, so existing engine/browser defaults still apply.

Test plan

• Unit tests added/updated
• Manual testing performed
• Documentation updated (not applicable)

Verification run:

• bunx vitest run packages/producer/src/services/render/captureBeyondViewport.test.ts
• bun --filter @hyperframes/producer typecheck
• bun run format:check
• bun run lint
• bunx vitest run packages/producer/src/services/render/captureBeyondViewport.test.ts packages/producer/src/services/renderOrchestrator.test.ts
• bun test --timeout 60000 packages/producer/src/services/distributed/renderChunk.test.ts
• bun --filter @hyperframes/producer build
• git diff --check

Note: I verified the source-level root cause and both affected call sites locally. I could not run the reporter's private benchmark suite from the issue thread, so the perf delta still needs validation on the same software-render host/fixture after merge.