v0.5.0: Trash (soft-delete) + Keep folder

Delete now moves an artifact to a recoverable Trash instead of hard-removing.

- Model: Artifact.deleted_at (nullable, indexed) = in Trash.
- Soft-delete everywhere: DELETE /api/artifacts/{id} sets deleted_at
  (idempotent 204); session POST /a/{id}/delete for the feed's hover Delete
  icon; POST /a/{id}/undelete restores; POST /feed/empty-trash purges.
- Trashed artifacts are off-quota (deleting frees quota) and eviction-protected
  (never evicted early); hidden from feed, sources, counts, and all API reads
  (list/detail/raw).
- Sidebar: "Deleted" and "Keep" system folders at the bottom (counts, hidden
  when empty); ?folder=deleted / ?folder=keep views reuse the row rendering.
  Deleted view has hover Undelete + an Empty Trash button. Keep = view over
  is_kept. Live-poll disabled in folder views.
- Docs (api.md delete section, CLAUDE.md), 10 new/updated tests. 150 passing;
  API soft-delete lifecycle verified live.

Purge is manual (Empty Trash) this release; auto purge-on-delete (background,
~3-day retention) is the planned fast-follow.

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

artifacts/storage.py

@@ -70,8 +70,13 @@ def artifact_total_bytes(artifact):
 
 
 def user_usage_bytes(user):
+    # Trashed artifacts are off-quota (deleting relieves quota immediately);
+    # their files linger on disk until Empty Trash / purge, but don't count.
     artifact_bytes = (
-        Artifact.objects.filter(owner=user).aggregate(total=Sum("size_bytes")).get("total") or 0
+        Artifact.objects.filter(owner=user, deleted_at__isnull=True)
+        .aggregate(total=Sum("size_bytes"))
+        .get("total")
+        or 0
     )
     asset_bytes = (
         Asset.objects.filter(owner=user).aggregate(total=Sum("size_bytes")).get("total") or 0
@@ -113,8 +118,10 @@ def make_room_for(user, incoming_bytes):
     if used + incoming_bytes <= quota:
         return []
 
+    # Trashed artifacts are eviction-protected (recovery window is guaranteed)
+    # and already off-quota, so they're never eviction candidates.
     unkept = list(
-        Artifact.objects.filter(owner=user, is_kept=False).order_by("created_at")
+        Artifact.objects.filter(owner=user, is_kept=False, deleted_at__isnull=True).order_by("created_at")
     )
     # Check whether eviction can possibly succeed before deleting anything -
     # otherwise a doomed request would still destroy every unkept artifact on
@@ -137,6 +144,16 @@ def make_room_for(user, incoming_bytes):
     return evicted
 
 
+def purge_trashed(user):
+    """Permanently remove all of a user's trashed artifacts (files + rows).
+    Backs the "Empty Trash" action."""
+    trashed = list(Artifact.objects.filter(owner=user, deleted_at__isnull=False))
+    for artifact in trashed:
+        delete_artifact_files(artifact)
+        artifact.delete()
+    return len(trashed)
+
+
 ASSET_ORPHAN_GRACE = timedelta(hours=24)