Run web builds before extension builds during deploy

[MitchLillie]

Problem

When deploying an app with [admin] static_root, the web build (e.g. Vite) and extension builds run in parallel via a single renderConcurrent call. The admin extension's include_assets step can attempt to copy files from static_root before the web build has finished populating it. Vite's emptyOutDir: true deletes dist/ at the start of its build, so the admin extension either sees a missing or empty directory and skips the copy. The result:

index_missing: index.html must be present in the bundle.

Solution

Split the single renderConcurrent call into two sequential phases:

1. Web builds first — run all web build processes (Vite, etc.) to completion
2. Extension builds second — run extension builds which may copy from web build output

Extensions within each phase still run concurrently with each other.

This makes the dependency between web builds and extensions explicit rather than relying on timing or polling.