Add Legacy Cancellation Support and Fix Stripe Webhook Verification for App Router

[Ashad001]

This pull request introduces support for handling legacy users who do not have proper Stripe subscription IDs in the subscription cancellation flow. The changes ensure that legacy users are processed differently, bypassing Stripe API calls and updating Redis directly. Key updates include adjustments to logic for determining user type, handling credits, and updating subscription statuses.

Enhancements for Legacy User Handling:

• Added isLegacyUser logic to identify users without valid Stripe subscription IDs and adjusted the cancellation flow to skip Stripe API calls for these users. (auto-analyst-frontend/app/api/trial/cancel/route.ts: [1] [2] [3]
• Updated Redis operations to immediately set credits to zero and mark subscriptions as canceled for legacy users. (auto-analyst-frontend/app/api/trial/cancel/route.ts: [1] [2]; auto-analyst-frontend/app/api/user/cancel-subscription/route.ts: [3]

Message and Status Updates:

• Adjusted cancellation response messages to differentiate between legacy users and trial or standard users. (auto-analyst-frontend/app/api/trial/cancel/route.ts: [1] [2]; auto-analyst-frontend/app/api/user/cancel-subscription/route.ts: [3]
• Updated subscription status handling to reflect immediate cancellation for legacy users versus scheduled cancellation for others. (auto-analyst-frontend/app/api/user/cancel-subscription/route.ts: auto-analyst-frontend/app/api/user/cancel-subscription/route.tsL34-R101)

These changes ensure a smoother cancellation process for legacy users while maintaining proper handling for standard and trial users.