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>

controlpanel/services/statistics.py

@@ -58,6 +58,7 @@ def club_statistics(club):
     return [
         {
             "title": "Members",
+            "icon": "users",
             "stats": [
                 ("Members", memberships.values("member").distinct().count()),
                 ("Active this season", memberships.filter(season=season, status=ClubMembership.StatusChoices.ACTIVE).count() if season else 0),
@@ -67,6 +68,7 @@ def club_statistics(club):
         },
         {
             "title": "Teams & staff",
+            "icon": "shield",
             "stats": [
                 ("Teams", Team.objects.filter(club=club).count()),
                 ("Players this season", TeamMembership.objects.filter(team__club=club, season=season).count() if season else 0),
@@ -75,6 +77,7 @@ def club_statistics(club):
         },
         {
             "title": "Events",
+            "icon": "calendar-days",
             "stats": [
                 ("Upcoming", events.filter(start__gte=now).count()),
                 ("This season", events.filter(season=season).count() if season else 0),
@@ -82,6 +85,7 @@ def club_statistics(club):
         },
         {
             "title": "Shop",
+            "icon": "shopping-cart",
             "stats": [
                 ("Orders", orders.count()),
                 ("Revenue", _money(orders.filter(status__in=PAID_STATUSES))),