refactor: flatten plans.features JSON to typed columns

The features JSON column required defensive fallback stubs in three
places (Plan::resolveForUser, PlanFeatures::__construct, PlanSeeder)
and silently swallowed misspelled keys. Typed columns give Eloquent
type-safe reads, simplify the Filament form (no more dotted JSON
paths), and let resolveForUser fail loud when the free row is
missing.

PlanFeatures public API is unchanged so consumers (jobs, middleware)
need no rewrites — one missed JSON read in SendScheduledWhatsAppJob
was caught and converted to a typed where() query.

tests/Pest.php seeds PlanSeeder in beforeEach so any feature test
that resolves a plan finds the free row, mirroring production where
plans always exist.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/Feature/Tiers/PlanResourceTest.php

@@ -43,12 +43,12 @@ it('saves email frequency on edit', function (): void {
 
     Livewire::test(EditPlan::class, ['record' => $plan->id])
         ->fillForm([
-            'features.email.frequency' => 'daily',
+            'email_frequency' => 'daily',
         ])
         ->call('save')
         ->assertHasNoFormErrors();
 
-    expect($plan->fresh()->features['email']['frequency'])->toBe('daily');
+    expect($plan->fresh()->email_frequency)->toBe('daily');
 });
 
 it('saves sms daily limit on edit', function (): void {
@@ -56,12 +56,12 @@ it('saves sms daily limit on edit', function (): void {
 
     Livewire::test(EditPlan::class, ['record' => $plan->id])
         ->fillForm([
-            'features.sms.daily_limit' => 3,
+            'sms_daily_limit' => 3,
         ])
         ->call('save')
         ->assertHasNoFormErrors();
 
-    expect($plan->fresh()->features['sms']['daily_limit'])->toBe(3);
+    expect($plan->fresh()->sms_daily_limit)->toBe(3);
 });
 
 it('saves null fuel type max for pro (unlimited)', function (): void {
@@ -69,10 +69,10 @@ it('saves null fuel type max for pro (unlimited)', function (): void {
 
     Livewire::test(EditPlan::class, ['record' => $plan->id])
         ->fillForm([
-            'features.fuel_types.max' => null,
+            'max_fuel_types' => null,
         ])
         ->call('save')
         ->assertHasNoFormErrors();
 
-    expect($plan->fresh()->features['fuel_types']['max'])->toBeNull();
+    expect($plan->fresh()->max_fuel_types)->toBeNull();
 });