Add pricing-page waitlist (name + email signup)

Replaces the disabled "Coming soon" buttons on the pricing page with a
waitlist band so visitors can be notified when alerts launch — separate
from registered users.

- waitlist_subscribers table (name, email unique, source, referrer)
- WaitlistService::subscribe — normalises email, idempotent
- Public POST /api/waitlist (throttle:10,1), thin controller + form request
- Read-only Filament resource with streamed CSV export
- Vue: useWaitlist composable + WaitlistForm, rendered below the grid
  while any tier is still "coming soon"; sends source + document.referrer

Announcement send mechanism deferred to a later task.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/Filament/Resources/WaitlistSubscriberResource.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace App\Filament\Resources;
+
+use App\Filament\NavigationGroup;
+use App\Filament\Resources\WaitlistSubscriberResource\Pages\ListWaitlistSubscribers;
+use App\Models\WaitlistSubscriber;
+use Filament\Resources\Resource;
+use Filament\Tables\Columns\TextColumn;
+use Filament\Tables\Table;
+
+class WaitlistSubscriberResource extends Resource
+{
+    protected static ?string $model = WaitlistSubscriber::class;
+
+    protected static string|\UnitEnum|null $navigationGroup = NavigationGroup::Users;
+
+    protected static ?string $navigationLabel = 'Waitlist';
+
+    protected static ?int $navigationSort = 3;
+
+    public static function canCreate(): bool
+    {
+        return false;
+    }
+
+    public static function table(Table $table): Table
+    {
+        return $table
+            ->columns([
+                TextColumn::make('name')
+                    ->searchable(),
+                TextColumn::make('email')
+                    ->searchable()
+                    ->copyable(),
+                TextColumn::make('source')
+                    ->badge()
+                    ->placeholder('—')
+                    ->toggleable(),
+                TextColumn::make('referrer')
+                    ->limit(40)
+                    ->placeholder('—')
+                    ->toggleable(isToggledHiddenByDefault: true),
+                TextColumn::make('created_at')
+                    ->label('Joined')
+                    ->dateTime('d M Y H:i')
+                    ->sortable(),
+            ])
+            ->defaultSort('created_at', 'desc')
+            ->recordActions([])
+            ->filters([]);
+    }
+
+    public static function getPages(): array
+    {
+        return [
+            'index' => ListWaitlistSubscribers::route('/'),
+        ];
+    }
+}