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/routers/__init__.py

@@ -0,0 +1,25 @@
+"""
+L2 Server Routers.
+
+Each router handles a specific domain of functionality.
+"""
+
+from . import auth
+from . import assets
+from . import activities
+from . import anchors
+from . import storage
+from . import users
+from . import renderers
+from . import federation
+
+__all__ = [
+    "auth",
+    "assets",
+    "activities",
+    "anchors",
+    "storage",
+    "users",
+    "renderers",
+    "federation",
+]