Feature: Implement Subscription-Based Paid Routes

[aserven]

This pull request introduces a new "subscription" type for paid routes, allowing users to create routes that grant access based on a recurring monthly payment.

Key Changes:

• Dashboard UI (cmd/server/templates/dashboard.html):
  • Added "Subscription" as an option in the "Type" dropdown when creating a new paid route.
  • Updated the tooltip for route types to include an explanation for subscriptions.
  • Added "Subscription" to the type filter in the "My Paid Routes" list.
  • Ensured "Subscription" type is correctly displayed in the list of routes.
  • Modified client-side JavaScript to hide the "Credits" input field when "Subscription" type is selected, defaulting credits to 1 (as subscriptions are time-based, not credit-based for access).
• Route Handling (routes/handler.go):
  • Enhanced the tryExistingPayment logic to support subscriptions:
    • For purchases with type "subscription", it now checks if the subscription is active (i.e., within one month of its creation date).
    • If the subscription is active, access is granted without decrementing credits.
    • If expired, the flow proceeds to a new payment.
• Route Service (routes/service.go):
  • Updated the CreatePaidRoute service method to validate the routeType, ensuring it's one of the allowed types ("credit" or "subscription").

This feature expands the monetization options for users by enabling time-based access to their paid routes alongside the existing credit-based and one-time payment models.