Fix dashboard route overwritten by home redirect when using tenant slug attribute

[leek]

Fixes #19582

Problem

When a panel uses ->tenant(Model::class, 'slug') with a tenant slug attribute, the Dashboard page route (filament.{panel}.pages.dashboard) is never registered. Instead, it's overwritten by the home redirect (RedirectToHomeController).

Root cause: Route::getLastGroupPrefix() returns the raw group prefix including binding syntax (admin/{tenant:slug}), but Laravel's RouteCollection indexes routes by the normalized URI without binding syntax (admin/{tenant}). The isset() check fails due to this key mismatch, so the guard thinks no root route exists and registers the home redirect — which overwrites the Dashboard.

Fix

Strip binding syntax from $rootUri before looking it up in the route collection:

// Before
$rootUri = trim(Route::getLastGroupPrefix(), '/') ?: '/';

// After
$rootUri = preg_replace('/\{(\w+):\w+\}/', '{$1}', trim(Route::getLastGroupPrefix(), '/')) ?: '/';

Tests

Added two tests that verify:

1. The dashboard route is registered when using a tenant slug attribute
2. The home redirect is not registered when the dashboard already occupies the root path

Both tests fail without the fix and pass with it. All existing route tests continue to pass.