feat: rebrand to Sexy, restyle logo with gradient icon and updated assets

- Rename brand from SexyArt to Sexy throughout i18n locale
- Apply primary→accent gradient to SVG icon stroke
- Remove brand name text from logo, icon-only display
- Switch logo font to Noto Sans bold (default), drop Dancing Script
- Update favicons, app icons, webmanifest, and add logo.svg

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

packages/frontend/src/lib/components/logo/logo.svelte

@@ -1,21 +1,7 @@
 <script lang="ts">
-  import { _ } from "svelte-i18n";
   import SexyIcon from "../icon/icon.svelte";
-
-  const { hideName = false } = $props();
 </script>
 
 <div class="relative">
-  <SexyIcon class="w-8 h-8 text-primary" />
+  <SexyIcon class="w-12 h-12" />
 </div>
-<span
-  class={`logo text-3xl text-foreground opacity-90 tracking-wide font-extrabold drop-shadow-x ${hideName ? "hidden sm:inline-block" : ""}`}
->
-  {$_("brand.name")}
-</span>
-
-<style>
-  .logo {
-    font-family: "Dancing Script", cursive;
-  }
-</style>