site: owner-only dashboard link in header, mobile menu and homepage (g then d from any page); /start skips the site chrome JS

- Header/footer moved to #lib/components/SiteChrome.svelte, returned by a universal
  +layout.ts load only for non-immersive pages, so /start and the book reader never
  download icon libraries, dropdowns or the bits-ui Sheet. /start: 36 -> 18 JS files,
  133 -> 78 KB gzip.
- Header logo is a hashed asset (inlined), so it is cached with the build.
- inlineStyleThreshold 4096: tiny page/component CSS is inlined into the HTML.
- Umami is not loaded on /start.

src/routes/+layout.ts

@@ -0,0 +1,12 @@
+import { isImmersive } from '#lib/chrome.js';
+import type { LayoutLoad } from './$types';
+
+// The site header/footer (icon libraries, dropdowns, the bits-ui Sheet) live in SiteChrome,
+// imported only for pages that show them. Immersive pages such as the /start new-tab
+// dashboard never download that code. Universal loads may return components.
+export const load: LayoutLoad = async ({ data, url }) => ({
+	...data,
+	Chrome: isImmersive(url.pathname)
+		? null
+		: (await import('#lib/components/SiteChrome.svelte')).default
+});