feat: add E2E test for complete blockchain notification workflow

[pimaster900]

Covers the full pipeline:
Blockchain Event → Listener → Validation → Database → Scheduler → Notification

50 tests across 7 describe groups:

• Stage 1: RPC response & event payload validation
• Stage 2: EventRegistry (in-memory store)
• Stage 3: In-memory and DB-backed deduplication
• Stage 4: NotificationAPI → SQLite persistence
• Stage 5: Scheduler dispatch, retry, and failure exhaustion
• Stage 6: DiscordNotificationService delivery
• Full pipeline: happy path + failure at each stage

Supporting changes:

• Extend @stellar/stellar-sdk mock with scvString/scvVoid ScVal types
• Add generateCorrelationId export to request-id util
• Add sanitizeForDiscord export to discord-notification service

Acceptance criteria:

• Complete workflow executes successfully in a test environment ✓
• Failure at each major stage is handled predictably ✓

Overview

Related Issue

Closes #

Changes

Verification

# e.g.
cd dashboard && npm test
cd listener && npm run typecheck && npm test
cd contract/contracts/hello-world && cargo test

How to Test

Checklist

• Branch is up to date with main
• Tests added/updated and all pass locally
• cargo fmt --all run (if Rust changes)
• npm run lint passes (if TypeScript changes)
• Documentation updated if behavior changed

closes #796

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