feat: add clear all app data flow and harden soroban event processing - #1437

Summary

• Add a complete Clear All App Data flow in Settings with confirmation handling.
• Add app-data synchronization and diagnostics redaction/export coverage.
• Harden Soroban event processing by wrapping duplicate checks and event upserts in a Prisma transaction.
• Update Soroban event worker tests to verify transactional behavior and duplicate-event handling.

Validation

• Frontend tests: 386 passed
• Backend tests: 404 passed, 16 skipped
• Frontend production build: passed
• Staged diff check: clean
• GitHub comparison: able to merge

Closes #190