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/base.html

@@ -14,7 +14,7 @@
         <div class="container">
             <a class="navbar-brand d-flex align-items-center" href="/">
                 <img src="{{ url_for('static', filename='logo.svg') }}" alt="Stegasoo" height="36" class="me-2">
-                <span class="fw-bold">Stegasoo</span>
+                <span class="fw-bold title-gold">Stegasoo</span>
             </a>
             <button class="navbar-toggler" type="button" data-bs-toggle="collapse" data-bs-target="#navbarNav">
                 <span class="navbar-toggler-icon"></span>