v0.7.1: in-app password change, custom labels, always-on folders

- Settings -> Account: change your own password (current + new), session
  preserved via update_session_auth_hash.
- Custom labels: per-user palette in Settings -> Labels; apply/remove from a
  message's ... menu (menu stays open, checkmark = applied). Labels are unified
  with tags; chip colours sync to the global TagColor. New Label model +
  migration 0017; POST /a/{id}/label (session, owner-scoped, palette-validated).
- Sidebar Keep/Deleted folders are now always shown; count badge only when
  non-empty. Updates the stale 'hide when empty' note in CLAUDE.md.

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

artifacts/urls.py

@@ -10,6 +10,7 @@ urlpatterns = [
     path("a/<str:artifact_id>/read", views.mark_artifact_read, name="artifact-mark-read"),
     path("a/<str:artifact_id>/keep", views.toggle_artifact_keep, name="artifact-toggle-keep"),
     path("a/<str:artifact_id>/share", views.toggle_artifact_share, name="artifact-toggle-share"),
+    path("a/<str:artifact_id>/label", views.toggle_artifact_label, name="artifact-toggle-label"),
     path("a/<str:artifact_id>/delete", views.delete_artifact, name="artifact-delete"),
     path("a/<str:artifact_id>/undelete", views.undelete_artifact, name="artifact-undelete"),
     path("feed/empty-trash", views.empty_trash, name="feed-empty-trash"),
@@ -28,6 +29,7 @@ urlpatterns = [
     path("settings/", views.settings_home, name="settings-home"),
     path("settings/account/", views.settings_account, name="settings-account"),
     path("settings/api-keys/", views.settings_api_keys, name="settings-api-keys"),
+    path("settings/labels/", views.settings_labels, name="settings-labels"),
     path("settings/users/", views.settings_users, name="settings-users"),
     path("settings/demo-data/", views.settings_demo_data, name="settings-demo-data"),
     path("settings/storage/", views.settings_storage, name="settings-storage"),