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/activities.py

@@ -0,0 +1,99 @@
+"""
+Activity routes for L2 server.
+
+Handles ActivityPub activities and outbox.
+"""
+
+import logging
+from typing import Optional
+
+from fastapi import APIRouter, Request, Depends, HTTPException
+from fastapi.responses import JSONResponse
+
+from artdag_common import render
+from artdag_common.middleware import wants_html, wants_json
+
+from ..config import settings
+from ..dependencies import get_templates, require_auth, get_user_from_cookie
+
+router = APIRouter()
+logger = logging.getLogger(__name__)
+
+
+@router.get("")
+async def list_activities(
+    request: Request,
+    offset: int = 0,
+    limit: int = 20,
+):
+    """List recent activities."""
+    import db
+
+    username = get_user_from_cookie(request)
+
+    activities = await db.get_activities(offset=offset, limit=limit)
+    has_more = len(activities) >= limit
+
+    if wants_json(request):
+        return {"activities": activities, "offset": offset, "limit": limit}
+
+    templates = get_templates(request)
+    return render(templates, "activities/list.html", request,
+        activities=activities,
+        user={"username": username} if username else None,
+        offset=offset,
+        limit=limit,
+        has_more=has_more,
+        active_tab="activities",
+    )
+
+
+@router.get("/{activity_id}")
+async def get_activity(
+    activity_id: str,
+    request: Request,
+):
+    """Get activity details."""
+    import db
+
+    activity = await db.get_activity(activity_id)
+    if not activity:
+        raise HTTPException(404, "Activity not found")
+
+    # ActivityPub response
+    if "application/activity+json" in request.headers.get("accept", ""):
+        return JSONResponse(
+            content=activity.get("activity_json", activity),
+            media_type="application/activity+json",
+        )
+
+    if wants_json(request):
+        return activity
+
+    username = get_user_from_cookie(request)
+    templates = get_templates(request)
+    return render(templates, "activities/detail.html", request,
+        activity=activity,
+        user={"username": username} if username else None,
+        active_tab="activities",
+    )
+
+
+@router.post("")
+async def create_activity(
+    request: Request,
+    user: dict = Depends(require_auth),
+):
+    """Create a new activity (internal use)."""
+    import db
+    import json
+
+    body = await request.json()
+
+    activity_id = await db.create_activity(
+        actor=user["actor_id"],
+        activity_type=body.get("type", "Create"),
+        object_data=body.get("object"),
+    )
+
+    return {"activity_id": activity_id, "created": True}