chore: rebrand ClubManager -> RosterChief, add lucide icons

The clubmanager.app domain was taken, so the platform is now RosterChief
(rosterchief.app). Renames the Django project package clubmanager/ ->
rosterchief/ (git tracks it as a move, so history follows), every
`from rosterchief.base import ...`, the settings/wsgi/asgi module paths,
env vars (ROSTERCHIEF_BASE_DOMAIN / ROSTERCHIEF_RP_NAME), the MFA adapter
(RosterChiefMFAAdapter), brand text, and the docs.

Two things were deliberately NOT swept:
- club.models.ClubManager stays: it is the Django manager *for Club*, not the
  brand. A blind rename would have silently broken it.
- Migrations are untouched (history is not rewritten). The only reference was a
  cosmetic help_text, so a normal AlterField migration carries the new domain.

Note the WebAuthn RP ID is the base domain, so moving to rosterchief.app
cryptographically invalidates any passkey enrolled under the old one; they
cannot be migrated and must be re-enrolled. Nothing is in production, so the
real cost is zero.

Add django-lucide (from bsiebens/lucide) for icons: the theme toggle now swaps
sun/moon against the effective theme, and the control panel gets icons on its
tabs, actions and stat groups. Its classifiers stop at Django 5.0, but that is
stale metadata — verified rendering on Django 6 / Python 3.14.

Also add formbuilder, shop and controlpanel to ruff's known-first-party list,
which had drifted behind the apps that landed.

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

club/migrations/0011_alter_club_slug.py

@@ -0,0 +1,18 @@
+# Generated by Django 6.0.6 on 2026-07-13 13:39
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('club', '0010_club_archived_at'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='club',
+            name='slug',
+            field=models.SlugField(blank=True, help_text='Drives subdomain / path resolution (e.g. ajax-united.rosterchief.app).', max_length=255, unique=True, verbose_name='slug'),
+        ),
+    ]