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/tenancy.py

@@ -58,7 +58,7 @@ class ClubTenantMiddleware:
             reset_current_club(token)
 
     def get_club(self, request) -> Club | None:
-        # Imported lazily: club.models imports clubmanager.base, which imports
+        # Imported lazily: club.models imports rosterchief.base, which imports
         # this module, so a top-level import would be circular.
         from .models import Club
 
@@ -78,7 +78,7 @@ class ClubTenantMiddleware:
         if not host:
             return None
 
-        base_domain = getattr(settings, "CLUBMANAGER_BASE_DOMAIN", "").lower().strip(".")
+        base_domain = getattr(settings, "ROSTERCHIEF_BASE_DOMAIN", "").lower().strip(".")
 
         if base_domain:
             # Only hosts under the configured base domain carry a tenant slug.