billboard applets: drop billboard- prefix from partials & ids; Most Recent → Most Recent Scroll; room_scroll → scroll — TDD

- Slug renames (mig 0004): billboard-my-scrolls → my-scrolls; billboard-my-contacts → my-contacts; billboard-most-recent → most-recent-scroll (name → "Most Recent Scroll"); billboard-notes → notes
- Partial filenames lose the `billboard-` token to mirror dashboard/gameboard convention; element ids follow (id_applet_my_scrolls, id_applet_my_contacts, id_applet_most_recent_scroll, id_applet_notes, id_applet_scroll); .applet-billboard-scroll → .applet-scroll
- View fn billboard.views.room_scroll → scroll; template apps/billboard/room_scroll.html → scroll.html (URL name `billboard:scroll` already correct)
- ITs + FTs updated to new identifiers; SCSS selectors retitled

Code architected by Disco DeDisco <discodedisco@outlook.com>
Git commit message Co-Authored-By:
Claude Sonnet 4.6 <noreply@anthropic.com>

src/apps/applets/migrations/0004_rename_billboard_applet_slugs.py

@@ -0,0 +1,56 @@
+"""Drop the legacy `billboard-` slug prefix from billboard applets and
+rename Most Recent → Most Recent Scroll.
+
+The `billboard-` prefix snuck into seed migration 0003 against intent — no
+other context (dashboard, gameboard, wallet, game-kit) prefixes its applet
+slugs with the context name, and slugs need to stay portable so users can
+later rearrange which page hosts which applet.
+"""
+from django.db import migrations
+
+
+RENAMES = [
+    # (old_slug,                new_slug,             new_name_or_None)
+    ('billboard-my-scrolls',    'my-scrolls',         None),
+    ('billboard-my-contacts',   'my-contacts',        None),
+    ('billboard-most-recent',   'most-recent-scroll', 'Most Recent Scroll'),
+    ('billboard-notes',         'notes',              None),
+]
+
+
+def _apply(apps, mapping):
+    Applet = apps.get_model('applets', 'Applet')
+    for old_slug, new_slug, new_name in mapping:
+        try:
+            applet = Applet.objects.get(slug=old_slug)
+        except Applet.DoesNotExist:
+            continue
+        applet.slug = new_slug
+        fields = ['slug']
+        if new_name is not None:
+            applet.name = new_name
+            fields.append('name')
+        applet.save(update_fields=fields)
+
+
+def forward(apps, schema_editor):
+    _apply(apps, RENAMES)
+
+
+def backward(apps, schema_editor):
+    inverse = [
+        (new, old, 'Most Recent' if old == 'billboard-most-recent' else None)
+        for (old, new, _) in RENAMES
+    ]
+    _apply(apps, inverse)
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('applets', '0003_seed_applets'),
+    ]
+
+    operations = [
+        migrations.RunPython(forward, backward),
+    ]