Polish UI styling across site

- Flip gradient to purple→blue (eggplant #4a2860 → blue #5570d4)
- Add gold title styling (.title-gold) for Stegasoo branding
- Style two-choice toggles with gradient-matched purple/blue colors
- Equal-width toggle buttons with hover highlight
- Tools page: green→amber tab gradient with dark background
- Dashed separator between toggle options

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontends/web/templates/index.html

@@ -9,7 +9,7 @@
         <div class="d-flex align-items-end justify-content-center gap-4">
             <img src="{{ url_for('static', filename='logo.svg') }}" alt="Stegasoo" height="155">
             <div style="margin-bottom: 40px;">
-                <h1 class="display-4 fw-bold mb-2">
+                <h1 class="display-4 fw-bold mb-2 title-gold">
                     Stegasoo
                     <span class="badge bg-success fs-6 ms-2">v4.0</span>
                 </h1>