feat(branding): customize your portal's logo, color, and theme

[canghai118]

What

Make the feedback portal yours from dashboard settings, with a live preview of the public portal as you edit.

For workspace owners:

• A Branding section under Portal settings to upload a logo, pick an accent color, set a default theme (light / dark / follow system), and write a welcome title + description for the portal home.
• A live mini-preview that re-renders the portal with your brand tokens as you change them — no save-and-reload loop.
• Your logo becomes the favicon on every surface (dashboard included), so the browser tab mirrors the brand you just set.

The accent color drives the portal's primary/accent tokens, derived in OKLCH for consistent foreground contrast in both light and dark, while neutrals stay a clean gray so backgrounds, cards, and borders match between the portal and the dashboard.

Implementation notes

• Branding lives in organization.metadata (no schema migration); the logo is stored via the upload service and surfaced through portal-identity.get.ts.
• Theme resolves server-side for light/dark (no FOUC); system is corrected before paint by a small inline script and kept in sync client-side.
• md-editor surfaces (welcome / post / comment bodies) bind their theme to a hydration-stable seed (useEditorTheme) so SSR and client agree — no hydration class mismatch.

Testing

End-to-end verified in a browser on a single-tenant default-org:

• Branding settings (logo, color, default theme, welcome title/description) save and persist to org metadata.
• Public portal reflects the brand color, honors the default theme on first paint (no FOUC), renders the welcome block markdown, and uses the logo as the favicon.
• Theme switcher (auto / light / dark) persists via cookie and is honored at SSR.
• Zero hydration warnings across portal home, post detail, and the dashboard settings pages.