Add modular app structure for L2 server

- Create app factory with routers and templates
- Auth, assets, activities, anchors, storage, users, renderers routers
- Federation router for WebFinger and nodeinfo
- Jinja2 templates for L2 pages
- Config and dependency injection

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

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

app/templates/auth/register.html

@@ -0,0 +1,45 @@
+{% extends "base.html" %}
+
+{% block title %}Register - Art-DAG{% endblock %}
+
+{% block content %}
+<div class="max-w-md mx-auto">
+    <h2 class="text-xl font-semibold mb-6">Register</h2>
+
+    <div id="register-result"></div>
+
+    <form hx-post="/auth/register" hx-target="#register-result" hx-swap="innerHTML" class="space-y-4">
+        <div>
+            <label for="username" class="block text-sm font-medium text-gray-300 mb-2">Username</label>
+            <input type="text" id="username" name="username" required pattern="[a-zA-Z0-9_-]+"
+                   class="w-full px-4 py-3 bg-gray-800 border border-gray-600 rounded-lg text-white focus:border-blue-500 focus:outline-none">
+        </div>
+
+        <div>
+            <label for="email" class="block text-sm font-medium text-gray-300 mb-2">Email (optional)</label>
+            <input type="email" id="email" name="email"
+                   class="w-full px-4 py-3 bg-gray-800 border border-gray-600 rounded-lg text-white focus:border-blue-500 focus:outline-none">
+        </div>
+
+        <div>
+            <label for="password" class="block text-sm font-medium text-gray-300 mb-2">Password</label>
+            <input type="password" id="password" name="password" required minlength="6"
+                   class="w-full px-4 py-3 bg-gray-800 border border-gray-600 rounded-lg text-white focus:border-blue-500 focus:outline-none">
+        </div>
+
+        <div>
+            <label for="password2" class="block text-sm font-medium text-gray-300 mb-2">Confirm Password</label>
+            <input type="password" id="password2" name="password2" required minlength="6"
+                   class="w-full px-4 py-3 bg-gray-800 border border-gray-600 rounded-lg text-white focus:border-blue-500 focus:outline-none">
+        </div>
+
+        <button type="submit" class="w-full px-4 py-3 bg-blue-600 hover:bg-blue-700 text-white font-medium rounded-lg">
+            Register
+        </button>
+    </form>
+
+    <p class="mt-6 text-gray-400">
+        Already have an account? <a href="/auth/login" class="text-blue-400 hover:text-blue-300">Login</a>
+    </p>
+</div>
+{% endblock %}