Stabilize isolated browser matrix

[HaithamAlMaamari]

Summary

• run each browser project sequentially against a fresh server and isolated quota state
• keep the supported npm command cross-platform through a Node matrix runner
• force the canonical SVG mark to remain one emitted asset across Vite 8.2
• make rerun heading focus resilient to delayed WebKit dialog restoration

Verification

• focused canonical asset browser assertion
• full Chromium and Firefox projects passed
• WebKit project passed twice consecutively after the focus fix
• format, unit tests, lint, and production build passed