Complete L1 router and template migration

- Full implementation of runs, recipes, cache routers with templates
- Auth and storage routers fully migrated
- Jinja2 templates for all L1 pages
- Service layer for auth and storage

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

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

app/templates/base.html

@@ -0,0 +1,23 @@
+{% extends "base.html" %}
+
+{% block brand %}Art-DAG L1{% endblock %}
+
+{% block nav_items %}
+<nav class="flex items-center space-x-6">
+    <a href="/runs" class="text-gray-300 hover:text-white {% if active_tab == 'runs' %}text-white font-medium{% endif %}">Runs</a>
+    <a href="/recipes" class="text-gray-300 hover:text-white {% if active_tab == 'recipes' %}text-white font-medium{% endif %}">Recipes</a>
+    <a href="/media" class="text-gray-300 hover:text-white {% if active_tab == 'media' %}text-white font-medium{% endif %}">Media</a>
+    <a href="/storage" class="text-gray-300 hover:text-white {% if active_tab == 'storage' %}text-white font-medium{% endif %}">Storage</a>
+</nav>
+{% endblock %}
+
+{% block nav_right %}
+{% if user %}
+<div class="flex items-center space-x-4">
+    <span class="text-gray-400">{{ user.username }}</span>
+    <a href="/auth/logout" class="text-gray-300 hover:text-white">Logout</a>
+</div>
+{% else %}
+<a href="/login" class="text-gray-300 hover:text-white">Login</a>
+{% endif %}
+{% endblock %}