feat(theme): per-theme brand logos (VNClagoon wordmark ↔ SRC mark)

Add optional logoLightUrl/logoDarkUrl to InstalledTheme + resolveThemeLogo()
helper; set logos on vnclagoon + src themes; login page and nav-rail prefer the
active theme's logo, falling back to the global config logo. So switching theme
switches the whole brand. 0 type errors.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

vnc/VNC-CHANGES.md

@@ -32,6 +32,11 @@ that merging new upstream releases stays a triage exercise, not an archaeology d
 | 2026-08-03 | `stores/theme-store.ts` | default `theme`/`resolvedTheme` → `dark` | dark-first per VNClagoon styleguide |
 | 2026-08-03 | `lib/builtin-themes.ts` | add `builtin-src` theme (Swiss red on white, light-first) | 2nd brand theme (SRC Advisory); VNClagoon stays default |
 | 2026-08-03 | `public/branding/src-logo.svg` (new) | SRC mountain mark | SRC brand (placeholder — swap official) |
+| 2026-08-03 | `lib/plugin-types.ts` | add optional `logoLightUrl`/`logoDarkUrl` to InstalledTheme | per-theme brand logos |
+| 2026-08-03 | `lib/theme-logo.ts` (new) | `resolveThemeLogo()` helper | pick active theme's logo, fall back to global |
+| 2026-08-03 | `lib/builtin-themes.ts` | set logos on vnclagoon (wordmark) + src (mark) | logo switches with the brand theme |
+| 2026-08-03 | `app/(main)/[locale]/login/page.tsx` | login logo uses active theme's logo | brand-switch on login |
+| 2026-08-03 | `components/layout/navigation-rail.tsx` | nav-rail logo uses active theme's logo | brand-switch in app |
 
 _Note: Vercel was tried and **abandoned** on 2026-08-03. Bulwark writes to a local
 data dir (`/app/data/*`); Vercel serverless has a read-only filesystem → crash