Migrate to GP247 2.0: TailAdmin/Livewire admin screen

The admin screen extended the now-deleted gp247-core::layout (AdminLTE)
with Bootstrap/jQuery form widgets, both removed in the 2.0 cutover.
Replaced with a custom GP247AdminComponent (not ConfigForm - the
3-provider x 4-field grouped-card layout doesn't fit ConfigForm's flat
key/value table) backed by the same admin_config group/code/key scheme
the legacy AdminController used, so already-configured provider
credentials keep working across the upgrade.

The client secret is never assigned to a public Livewire property (those
serialize into the page for client-side hydration) - only a boolean
hasSecret flag is exposed, preserving the legacy screen's masked-secret,
leave-blank-to-keep-existing behavior without leaking it into the page
source.

Collapsed the two legacy routes (GET index, POST save) into one Livewire
route. Removed unused scaffold leftovers (Controllers/FrontController.php,
Views/Front.blade.php, Views/script.blade.php) that were never wired to
any route. Bump gp247.json to version 2.0 / requireCore 2.0, and updated
both readmes accordingly.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>