Feat: Unified Notification System with Smart Alerting

[memplethee-lab]

Closes #42

Summary

Adds smart notification alerting for blockchain events, including Telegram and Discord delivery, user preference routing, throttling, deduplication, and analytics tracking.

Related Issues

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that changes existing behaviour)
• Documentation only
• Refactor / chore (no functional change)

Changes

• Add Telegram notification provider.
• Add Discord webhook notification provider.
• Add Telegram and Discord notification channels.
• Add configurable blockchain alert rules.
• Add alert rule evaluation and affected-user resolution.
• Add notification throttling and event deduplication with Redis.
• Add notification analytics and delivery metrics.
• Route alerts through enabled user notification preferences.
• Register the new providers and alerting services in the notifications module.
• Add required notification dependencies and type definitions.

Checklist

• I have read the CONTRIBUTING guide.
• npm run lint passes.
• npx tsc --noEmit passes (no type errors).
• npm run build succeeds.
• npm test passes, and I added/updated tests for my change where it
  made sense.
• Any Stellar/Soroban network access goes through the stellar module
  services (no direct Horizon/RPC calls from feature modules).
• I did not commit secrets, private keys, or mainnet credentials.

Notes for Reviewers

• Telegram delivery requires TELEGRAM_BOT_TOKEN.
• Discord delivery requires DISCORD_WEBHOOK_URL.
• External providers remain disabled when their credentials are not configured.
• The feature uses Redis for blockchain event subscription, throttling,
  deduplication, and analytics counters.
• npm run build was verified successfully.
• Lint, typecheck, and test commands were not run as part of this change.