refactor: UX and styling improvements across frontend

- Fix login spinner (isLoading never set to true before await)
- Extract PageHero component, replace copy-pasted hero sections on videos/models/tags pages
- Replace inline plasma blobs with SexyBackground on videos/models/tags pages
- Make video/model/tag cards fully clickable (wrap in <a>), remove redundant Watch/View Profile buttons
- Convert inner overlay anchors to divs to avoid nested <a> elements
- Fix home page model avatar preset: mini → thumbnail (correct size for 96px display)
- Reduce home hero height: min-h-screen → min-h-[70vh]
- Remove dead hideName prop from Logo, simplify component
- Add brand name to mobile flyout panel header with gradient styling
- Remove dead _relatedVideos array, isBookmarked state, _handleBookmark from video detail page
- Clean up commented-out code blocks in video detail and models pages
- Note: tag card inner tag links converted to spans to avoid nested anchors

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

packages/frontend/src/lib/components/page-hero/page-hero.svelte

@@ -0,0 +1,32 @@
+<script lang="ts">
+  import type { Snippet } from "svelte";
+
+  interface Props {
+    title: string;
+    description?: string;
+    children?: Snippet;
+  }
+
+  let { title, description, children }: Props = $props();
+</script>
+
+<section class="relative py-12 md:py-20 overflow-hidden">
+  <div class="absolute inset-0 bg-gradient-to-br from-primary/10 via-accent/5 to-background"></div>
+  <div class="relative container mx-auto px-4 text-center">
+    <div class="max-w-5xl mx-auto">
+      <h1
+        class="text-5xl md:text-7xl font-bold mb-6 bg-gradient-to-r from-primary via-accent to-primary bg-clip-text text-transparent"
+      >
+        {title}
+      </h1>
+      {#if description}
+        <p class="text-xl md:text-2xl text-muted-foreground mb-10 leading-relaxed max-w-4xl mx-auto">
+          {description}
+        </p>
+      {/if}
+      {#if children}
+        {@render children()}
+      {/if}
+    </div>
+  </div>
+</section>