fix: show course price in its own currency on catalog about sidebar

[choeying-10]

Summary

• Catalog About sidebar showed "Free" for paid non-USD courses because get_course_prices() forces PAID_COURSE_REGISTRATION_CURRENCY (USD) and falls back to "Free" on a currency mismatch.
• Added get_course_display_price() in common/djangoapps/course_modes/models.py that reads the course's own paid mode (verified preferred, else first paid mode) and formats min_price with that mode's own currency symbol via Babel.
• Wired it into CoursewareMeta.course_price (courseware_api/views.py). get_course_prices() is untouched for all other callers; genuinely free courses still return "Free".

Behavior

• Paid USD course: $1000 (unchanged)
• Paid INR/EUR/etc course: ₹1000 / €40 (was "Free")
• Free course: "Free" (unchanged)

Verified

• Catalog About sidebar shows correct currency+price for all the currencies.
• Free course shows "Free"

[choeying-10]

Findings: Open edX ecommerce direction + the catalog price fix

The strategic direction: LMS should NOT own pricing

• Open edX's stated approach is to not maintain its own commerce service, but to expose a robust set of APIs/hooks to integrate best-of-breed external systems. WooCommerce is the reference implementation.

• Ecommerce Integration wiki: https://openedx.atlassian.net/wiki/spaces/OEPM/pages/4523261967/Ecommerce+Integration

• The key statement of intent (from the Oct 4, 2024 community design): the LMS "would not have any knowledge of concepts like bundles, discounts, offers, or even prices." (same wiki page above)

• The newer In-App Purchases proposal reinforces it: a thin Purchase Gateway + provider (RevenueCat/Stripe), where "prices come from store metadata/provider offerings (never hard-coded)" — i.e., the client fetches price from the external store, not the LMS.

• [Proposal] In-App Purchases for Open edX (Purchases & Upgrades) openedx/platform-roadmap#476

Important caveat: gradual, hook-based, no firm timeline

• Maintainers explicitly said removal will be gradual and that they will likely add filters/hooks so operators can plug in their own commerce system for pricing lookups before pricing is removed from the platform.

• Discussion thread: https://discuss.openedx.org/t/deprecation-removal-ecommerce-service-depr-22/6839

• (Oscar deprecation Q&A): https://discuss.openedx.org/t/oscar-based-ecommerce-stack-deprecation/13760