feat: Configure AI usage counter

[kofimokome]

Fixes #7

[sourceant]

Code Review Summary

This PR introduces AI usage tracking and Stripe-based billing using Laravel Cashier. It includes migrations for usage counters and billing entities, a service for entitlement management, and a checkout controller.

🚀 Key Improvements

• Integrated Laravel Cashier for subscription management.
• Implemented an idempotency check for token consumption using Laravel Cache.
• Added OpenAPI (Swagger) documentation for the new checkout endpoint.

💡 Minor Suggestions

• Standardize config keys in cloudplans.php.
• Use explicit dependency injection for usage tracking instead of backtraces.

🚨 Critical Issues

• Stripe webhook endpoint lacks signature verification middleware.
• Potential 'Undefined index' in CloudController when region is missing from config.

[sourceant]

Review complete. See the overview comment for a summary.

[sourceant]

The keys 'monthly_price_id' and 'yearly_price_id' should be consistent across all regions and should preferably use ENV variables instead of hardcoded 'plan_id' or 'price_id' placeholders to ensure security and flexibility across environments.

Suggested change

	'monthly_price_id'=>'plan_id', // from stripe
	'monthly_price_id' => env('STRIPE_MONTHLY_PRICE_ID_US'),
	'monthly_price' => (float) env('CLOUD_PLAN_MONTHLY_PRICE_US', 5.00),
	'yearly_price' => (float) env('CLOUD_PLAN_YEARLY_PRICE_US', 50.00),
	'yearly_price_id' => env('STRIPE_YEARLY_PRICE_ID_US'),

[sourceant]

Using debug_backtrace to implement idempotency is highly discouraged. It is slow and relies on internal call structures that may change. Pass the message ID or an idempotency token explicitly to the consume method instead.

Suggested change

	private function getCurrentChatMessageId(): ?int
	// Recommended: Pass the unique identifier directly to the consume method.
	// If that is not possible, ensure ProcessChatMessageJob is always present in the stack.