Import Tripoli Cloud frontend prototype

React/TypeScript/Vite/Tailwind prototype from the design session (login,
dashboard, photos, backups, settings views with mocked API layer).
Infra work (Rust services, Ansible, OpenTofu) follows in subsequent commits.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/src/lib/backgrounds.ts

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+/**
+ * Auth-screen background layers. Replace each entry with
+ * `url('/assets/bg-1.jpg') center/cover no-repeat` for real photography —
+ * the crossfade logic in useBackgroundCrossfade doesn't change.
+ */
+export const BACKGROUND_IMAGES: string[] = [
+  'radial-gradient(120% 95% at 22% 12%, #2b3340 0%, #121620 55%, #070910 100%)',
+  'radial-gradient(120% 95% at 78% 18%, #2f2b3f 0%, #16131f 55%, #08070d 100%)',
+  'radial-gradient(130% 100% at 45% 85%, #1f3340 0%, #0f161c 55%, #070a0d 100%)',
+];

app/src/lib/gradients.ts

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+/** Shared placeholder-thumbnail gradients — swap for real thumbnails once assets exist. */
+export function tone(a: string, b: string): string {
+  return `linear-gradient(140deg, ${a} 0%, ${b} 100%)`;
+}
+
+export const THUMB_TONES = [
+  tone('#3b4a63', '#1b2230'),
+  tone('#4a3f5f', '#221c2e'),
+  tone('#5a4436', '#261d18'),
+  tone('#33505a', '#182428'),
+  tone('#46384f', '#1f1a24'),
+  tone('#3d4a41', '#1b211d'),
+  tone('#3a4560', '#1a1f2c'),
+  tone('#51413a', '#241d19'),
+] as const;

app/src/lib/validators.ts

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+const EMAIL_RE = /^[^@\s]+@[^@\s]+\.[a-z]{2,}$/i;
+
+export function isValidEmail(value: string): boolean {
+  return EMAIL_RE.test(value);
+}
+
+export function isValidPassword(value: string): boolean {
+  return value.length >= 8;
+}