Accounts Receiveable (AR) Export - Add additional fields

🔍 Problem Statement
As a finance admin, I experience the AR export missing key fields needed for collections follow-up on corporate subscribers, which requires manual cross-referencing across multiple reports.

💡 User Story
As a finance admin, I want the AR export to include billing contact, due date, and plan details, so that I can work the collections queue without supplementary data pulls.

🎯 Definition of Done
- Given the AR Export, when downloaded, then it includes: billing email, invoice due date, plan name, and subscriber contact name.
- This change impacts the API (AR export endpoint) and admin export UI.
- Limitations: fields are added to the existing CSV format; no new export type is created.

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Problem Statement: We rely on the Accounts Receivable (AR) Export in order to perform collections on our Corporate Subscribers. However, this export is missing a few key fields that would allow us to proactively address resulting downstream issues that we currently face. Key points to understand: At a Global setting level we allow a 30 day time period before a invoice goes uncollectible. For Corporate Subscriptions, each subscription typically carries a distinct plan (as it is a custom price point). The Days Before Uncollectible has an override of 180 days for each plan pertaining to a Corporate Subscription. Thus Corporate subscribers enjoy a total of 210 days before the Invoice moves to an “Uncollectible Status” and Subscription gets cancelled. In 80% of the cases where the subscription has gone uncollectible we end up reinstating the subscription by creating a new plan because the customer pays. This creates a lot of misleading and error prone accounting/finance entries. Requested Solution: Add the following fields to the Export Invoice Due Date - The Date the current Invoice will be due. We need this to help us identify when an invoice is due and help us prioritize our collection efforts based on the age of the invoice. Plan Auto Uncollectable Days - For each invoice, identify the Plan attached to the invoice and export the Plan level Auto Uncollectible Days value. This will allow us to compute the days (based on Invoice Due Date + Overide Uncollectible Days) remaining before the invoice would become uncollectible. Further, it gives us an opportunity to adjust the plan auto-uncollectible days value so that the invoice doesn’t go uncollectible and more vigorous follow up with the Customer and Sales Rep can be done to collect the money. This would also avoid downstream problems with reinstatement or payment application that we mentioned above. It would also allow us to identify if a Sales Rep has missed adding the Plan Level override for Auto-uncollectible days. Plan ID : The plan id attached to the invoice. This allows us to quickly identify which plan needs to be modified if needed (see 2. above). Sales rep name attached to the Subscription for which the Invoice is generated. — This allows our AR team to consult with the sales rep about upcoming invoices that are at a risk of going uncollectible and also identifying which Sales Reps are neglecting to ensure the Auto Uncollectible Days value and quickly correct those plans.