Fix governance events and migration lock

[Rampop01]

Description

This PR resolves two backend issues:

1. Issue [Backend] Indexer ignores fee_config_updated and admin_transferred governance events #524 [Backend] Indexer ignores fee_config_updated and admin_transferred governance events: Added indexing and SSE broadcasting for fee_config_updated and admin_transferred contract governance events. Used an elegant, referentially safe streamId = 0 system stream fallback to preserve Prisma schema integrity and foreign-key constraints.
2. Issue [Backend] migration_lock.toml declares sqlite but the datasource is postgresql, breaking prisma migrate #525 [Backend] migration_lock.toml declares sqlite but the datasource is postgresql: Fixed a production-blocking validation mismatch in Prisma by changing provider from "sqlite" to "postgresql" in migration_lock.toml.

Type of Change

• 🐛 Bug fix (non-breaking change which fixes an issue)
• ✨ New feature (non-breaking change which adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📚 Documentation update
• 🔧 Refactoring (no functional changes)
• ⚡ Performance improvement
• 🧪 Test addition or update

Related Issues

Closes #524
Closes #525

Changes Made

• Database Configuration:
  • Updated provider in backend/prisma/migrations/migration_lock.toml to "postgresql".
• Worker Indexer (soroban-event-worker.ts):
  • Added decodeU32 helper function to decode u32 event values.
  • Implemented ensureSystemStream to upsert a system user and stream with streamId = 0 during transaction callbacks to prevent database foreign-key constraint violations when writing protocol-level events.
  • Modified processEvent to allow single-topic events (topic.length === 1) for the two new protocol events while keeping the streamId requirement for per-stream events.
  • Implemented handleFeeConfigUpdated and handleAdminTransferred handlers to write records of types FEE_CONFIG_UPDATED and ADMIN_TRANSFERRED and broadcast payloads over the SSE admin channels stream.fee_config_updated and stream.admin_transferred.
• Classification Lists:
  • Added FEE_CONFIG_UPDATED and ADMIN_TRANSFERRED to allowed list arrays in events.routes.ts (EVENT_TYPES) and stream.controller.ts (validEventTypes).
• Syntax and Compile Fixes:
  • Resolved a pre-existing syntax error (missing arrow function opening brace {) in backend/tests/integration/stream-actions.test.ts to allow the test runner to compile all files.

Testing

Test Coverage

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Test Steps

1. Run mocked event worker unit tests validating governance event decoding, database upserts, and SSE broadcast trigger:

   npx vitest run tests/soroban-event-worker.test.ts

2. Run database-mocked integration tests asserting the event lifecycle:

   DATABASE_URL=postgresql://localhost/flowfi npx vitest run src/__tests__/integration/streams.test.ts

3. Verify that the Prisma migrate status check successfully resolves schema and migration lock providers without crashing:

   DATABASE_URL=postgresql://localhost/flowfi npx prisma migrate status

Breaking Changes

Screenshots/Demo

Checklist

• My code follows the project's style guidelines
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published
• I have checked for breaking changes and documented them if applicable

Additional Notes