fix: use appType "custom" for Vite dev server so worktree branding is applied

Vite's "spa" appType adds its own SPA fallback middleware that serves
index.html directly, bypassing the custom catch-all route that calls
applyUiBranding(). Changing to "custom" lets our route handle HTML
serving, which injects the worktree-colored favicon and banner meta tags.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/src/app.ts

@@ -242,7 +242,7 @@ export async function createApp(
     const { createServer: createViteServer } = await import("vite");
     const vite = await createViteServer({
       root: uiRoot,
-      appType: "spa",
+      appType: "custom",
       server: {
         middlewareMode: true,
         hmr: {