fix: replace inline SVGs with $icon() helper (FE-002)

Convert 90 inline SVG icons to use the shared $icon() helper function
across shop and vendor templates for consistency and maintainability.

Templates updated:
- Shop: checkout, products, login, register, forgot/reset-password
- Shop account: addresses, dashboard, messages, order-detail, orders, profile
- Vendor: billing, login, onboarding, team, landing pages (4 variants)

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

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

app/templates/vendor/landing-default.html

@@ -1,4 +1,5 @@
 {# app/templates/vendor/landing-default.html #}
+{# standalone #}
 {# Default/Minimal Landing Page Template #}
 {% extends "shop/base.html" %}
 
@@ -39,9 +40,7 @@
                        class="inline-flex items-center justify-center px-8 py-4 text-lg font-semibold rounded-lg text-white bg-primary hover:bg-primary-dark transition-colors shadow-lg hover:shadow-xl"
                        style="background-color: var(--color-primary)">
                         Browse Our Shop
-                        <svg class="w-5 h-5 ml-2" fill="none" stroke="currentColor" viewBox="0 0 24 24">
-                            <path stroke-linecap="round" stroke-linejoin="round" stroke-width="2" d="M14 5l7 7m0 0l-7 7m7-7H3"></path>
-                        </svg>
+                        <span class="w-5 h-5 ml-2" x-html="$icon('arrow-right', 'w-5 h-5')"></span>
                     </a>
                     {% if page.content %}
                     <a href="#about"