IA-987:feat(invoice): extend invoice-paid notification with billing details and...

Summary

Extends the invoice-paid notification with richer billing fields and migrates the Thymeleaf email template from the local project to S3, centralizing template management outside the codebase.

Changes

• InvoiceNotificationService – added pdfUrl, receiptNumber, periodStart, periodEnd, and planName to sendInvoicePaidEmail
• InvoiceNotificationServiceImpl – removed direct SpringTemplateEngine + ResourceBundleMessageSource usage (which resolved and rendered the local template); replaced with the shared EmailService + EmailTemplateConstants abstraction which fetches the template from S3 at send time
• InvoicePaidNotificationRequest – added the five new fields to the DTO
• NotificationController – updated /invoice-paid to forward the new fields to the service

Motivation

Moving the template to S3 allows content updates (wording, layout, branding) without requiring a redeployment. The local Thymeleaf rendering pipeline is no longer needed as the EmailService abstraction handles template fetching and rendering against S3-hosted templates.

Notes

• The invoice HTML template has been removed from the project resources and uploaded to S3
• All new fields are null-safe with sensible fallbacks
• URL fields are &-escaped to handle special characters safely in HTML email bodies