refactor: devbox service from go to nextjs

[mlhiter]

• docs(devbox): add frontend project guide
• build(devbox): align frontend dependencies
• feat(db): support PostgreSQL Prisma schema
• build(devbox): wire frontend runtime config
• feat(api): add v2alpha DevBox routes
• feat(template): persist editable defaults
• feat(ide): support filtered IDE menu
• fix(import): normalize startup command newlines
• feat(create): sync GPU and runtime form
• feat(ui): sync DevBox pages with release v5.1
• fix(api): standardize autostart errors
• fix(ci): restore frontend verify target
• refactor(v1): inline registry retag flow
• refactor(v2): inline registry retag flow
• docs: update devbox registry env guidance