chore(vst-host): delete monorepo package, repoint at published PyPI package

[vanceingalls]

What

Deletes packages/vst-host from the monorepo — it now lives as a standalone GPL-3.0 repo (heygen-com/hyperframes-vst-host), published to PyPI as hyperframes-vst-host (uv tool install hyperframes-vst-host puts hyperframes-vst on PATH). Arm's-length IPC (spawn/socket) keeps the GPL/Apache license boundary intact either way.

Simplifies resolveVstHostCommand in both vstBounce.ts (engine) and vstSidecar.ts (studio-server) from a 3-step precedence (env override → monorepo uv run --project → bare PATH) down to 2 steps (env override → bare PATH), since the monorepo path can never resolve again post-deletion. Updates vstRenderParity.test.ts's skip condition to probe for the installed hyperframes-vst CLI instead of a local packages/vst-host checkout, so the integration test keeps running wherever the package is installed rather than silently skipping forever. Repoints doc-comments that pointed at packages/vst-host source paths to the new repo.

Why

Finishes the repo split: the sidecar's GPL dependency (pedalboard) and its own release/versioning cadence don't belong bundled in this Apache-2.0 monorepo.

Test plan

• fallow audit passes clean
• Full monorepo build succeeds
• Full test suite passes across studio/engine/cli/studio-server/producer (vstRenderParity.test.ts correctly skips without the sidecar on PATH, and was separately verified to pass for real against the installed PyPI package)

🤖 Generated with Claude Code

[vanceingalls]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(studio): gate the VST FX section behind STUDIO_VST_ENABLED #2605
• chore(vst-host): delete monorepo package, repoint at published PyPI package #2604 👈 (View in Graphite)
• refactor(vst): split oversized files and dedupe CLI/engine code to clear fallow gate #2603
• feat(vst): voiceover spectral-carve VST pipeline (V1) #2602
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[vanceingalls]

Superseded by a recut stack: #2919 → #2920 → #2921 → #2922 → #2923.

Same net result (68 files, +8,632/-491) with the add-then-delete churn removed and rebased onto current main (this stack's merge-base was 519 commits behind). Leaving these open until the new stack is reviewed.

Per-PR deletions now: 122 (a net-negative refactor), 1, 297, 15, 54 — all real edits against main, none of it code an earlier PR in the stack had added.

[vanceingalls]

Closing in favor of the recut stack: #2919 → #2920 → #2921 → #2922 → #2923.

Same net result (68 files, +8,632/-491), rebased onto current main, with the add-then-delete churn removed — packages/vst-host/ is never added and then deleted, files arrive pre-split, and the feature flag lands with the first studio commit instead of trailing the stack.

Branches are left in place; nothing is deleted.