feat: implement multi-currency support for donation notifications, summaries, and analytics

[GBOYEE]

Closes #115

Summary

Implements full multi-currency support across the donation workflow. All changes are minimal and focused.

What changed

Prisma Schema (prisma/schema.prisma):

• Added conversion metadata fields to Donation model: baseCurrency, exchangeRate, convertedAmount, conversionTimestamp
• Added @@index([currency]) for efficient currency-based filtering

Notifications (src/services/notification.service.ts):

• sendDonationReceivedNotification now accepts currency param (defaults to XLM for backward compatibility) — displays e.g. "50 USDC" instead of always "XLM"
• sendDistributionSentNotification — same treatment
• Donation notifications include { amount, currency, campaignTitle } in metadata
• Updated tests to verify correct currency display

Notification Controller (src/controllers/notification.controller.ts):

• Passes currency from request body through to notification service

Email Worker (src/workers/email.worker.ts):

• Passes currency through job data for DONATION_RECEIVED and DISTRIBUTION_SENT jobs

Donation Service (src/services/donation.service.ts):

• Stores conversion metadata (baseCurrency, exchangeRate, convertedAmount, conversionTimestamp) when creating donations
• Supports currency filter in getDonationFilters

Donation Controller (src/controllers/donation.controller.ts):

• currency query parameter supported on all donation list endpoints (list, my-donations, campaign-donations)

Analytics Service (src/services/analytics.service.ts):

• Campaign analytics: donations and distributions grouped by currency → new byCurrency field
• Donor analytics: donations grouped by currency → new byCurrency field
• Organization analytics: funds grouped by currency → new byCurrency field

Types (src/types/index.ts):

• DonationFilters now includes optional currency field
• DonationInput now includes optional conversion metadata fields

Acceptance Criteria

• All hardcoded XLM assumptions removed from donation notification logic
• Notifications display the correct donation currency
• Donation summaries correctly handle multiple currencies (grouped by currency)
• Analytics support multi-currency reporting without mixing raw values
• Conversion metadata is stored at donation creation time
• Existing tests updated and new tests cover multi-currency scenarios
• No regression for existing XLM donation flows (backward compatible defaults)

[GBOYEE]

I'd like to work on this issue. I have background in devops and will submit a PR ASAP.

[GBOYEE]

I'd like to work on this issue. I have background in devops and will submit a PR ASAP.

[BarryArinze]

Resolve conflict

[GBOYEE]

Done — rebased on top of upstream/master and resolved the conflict. The branch is now clean and mergeable. Ready for review!

[GBOYEE]

Closing — issue assigned to another contributor