feat: Sentry Integration for Full Observability

[JudahSan]

Summary

Adds Sentry for error and performance monitoring, with secure setup and environment-aware configuration.

Key Features

• Configurable via environment variables.
• Smart sampling: critical endpoints (auth, core content) traced at higher rates, health checks skipped.
• Errors enriched with user, request, and release context.
• Sensitive data (e.g., password, token, api_key) scrubbed automatically.
• Releases linked to git commits for traceability.
• Safe integration: fails gracefully without credentials.

Why this Change?

Enables proactive monitoring and faster debugging without affecting app performance.

How to Test

1. Update config/credentials/development.yml.enc with valid Sentry credentials (sentry.dsn, sentry.enabled, optional rates).
2. Start your Rails server (rails server).
3. Follow the verification steps in the Sentry Rails docs to confirm events are sent successfully.