v0.7.0: mark all as read by clicking the unread badge

- Click a source's unread count in the sidebar to mark all of that source's
  messages read (clears the badge + reduces the All-sources total); click the
  All-sources total to mark everything read.
- POST /feed/mark-read (session, owner-scoped, excludes trashed). Visible feed
  rows drop their unread state too. Badge is keyboard-activatable (Enter/Space).

156 tests pass (4 new); inline JS re-validated with node --check.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

artifacts/views.py

@@ -696,6 +696,21 @@ def empty_trash(request):
     return JsonResponse({"purged": count})
 
 
+@login_required
+@require_POST
+def mark_all_read(request):
+    """Mark all of the user's unread (non-trashed) messages as read, optionally
+    scoped to one source. Backs the sidebar 'Mark all as read' action."""
+    unread = Artifact.objects.filter(
+        owner=request.user, deleted_at__isnull=True, read_at__isnull=True
+    )
+    source = request.POST.get("source", "")
+    if source:
+        unread = unread.filter(source=source)
+    marked = unread.update(read_at=timezone.now())
+    return JsonResponse({"marked": marked, "source": source})
+
+
 @login_required
 def feed_older(request):
     """Return the next page of older day-groups as an HTML fragment for infinite scroll."""