Tenant admins can now customize their workspace appearance: page/nav
backgrounds (solid, gradient, or image), column/card colors, borders,
text, opacity with glass blur, card corner radius, and accent colors.
Light and dark mode are configured separately. Theme CSS is injected
server-side via transformPageChunk to prevent FOUC.
Includes avatar components, account page updates, and pre-existing
type error fixes (Buffer, async onMount, InputJsonValue).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>