Fix Turbopack whole-project tracing from ffmpeg spawn calls

[richiemcilroy]

The dynamic ffmpeg path from getFfmpegPath() made Turbopack's output tracer fall back to tracing the entire project (including public/ and all CSS) into the serverless output for /api/tools/loom-download, /api/video/og, and the workflow step route.

This had two consequences:

1. The build warnings pasted in the deploy log (5 spawn call sites plus a dynamic fs.readFile), and bloated serverless functions.
2. The production deploy failure on main: the over-trace pulled app/globals.css and packages/ui/style/styles.css into the App Route module graph, where PostCSS evaluation failed with TypeError: __turbopack_context__.a is not a function and killed the build. The failing deploy's import trace shows globals.css reached via lib/video-convert.ts from the loom-download route, which is exactly this over-trace.

Fix: annotate all seven call sites (4 spawns in lib/audio-extract.ts, 1 spawn + 1 readFile in lib/video-convert.ts, 1 spawn in lib/og/poster-frame.ts) with turbopackIgnore. Safe because the ffmpeg binary still ships explicitly via serverExternalPackages + outputFileTracingIncludes in next.config.

Verified with a full local @cap/web build: tracing warnings went from seven to zero.

Greptile Summary

This PR adds Turbopack tracing-ignore annotations to dynamic ffmpeg spawn calls and a runtime temporary-file read, preventing whole-project serverless tracing while retaining explicit ffmpeg packaging.

• Annotates four ffmpeg spawn sites in the audio extraction utilities.
• Annotates the poster-frame and video-conversion ffmpeg spawn sites.
• Excludes the runtime-created converted-video path from static output tracing.

Confidence Score: 5/5

The PR appears safe to merge, with no concrete blocking or non-blocking defects identified in the changed code.

The annotations affect build-time output tracing only; runtime spawn arguments remain unchanged, the ignored file is always created dynamically in temporary storage, and explicit ffmpeg packaging remains configured.

Important Files Changed

Filename	Overview
apps/web/lib/audio-extract.ts	Adds tracing-ignore annotations to four existing dynamic ffmpeg spawn calls without changing their runtime arguments or process handling.
apps/web/lib/og/poster-frame.ts	Excludes the dynamic ffmpeg executable from Turbopack tracing while preserving poster-frame extraction behavior.
apps/web/lib/video-convert.ts	Excludes the dynamic ffmpeg executable and runtime-created temporary output path from static tracing without altering conversion or cleanup behavior.

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