feat(sentry): integrate Sentry for error tracking and performance mon…

[A-one-tech]

closes #23

PR: Add Sentry Error Tracking Integration

Summary

This PR integrates Sentry into the NestJS backend for centralized error reporting, performance tracing, and production monitoring.

What changed

• Added src/config/sentry.ts to initialize Sentry with DSN, environment, release, traces sampling, and uncaught exception / unhandled rejection handling.
• Added src/common/middleware/sentry.middleware.ts to capture request-level breadcrumbs for request method, path, params, and query context.
• Updated src/main.ts to initialize Sentry during bootstrap and register request/tracing middleware.
• Enhanced src/common/filters/global-exception.filter.ts to report server errors and auth failures to Sentry with request tags and correlation IDs.
• Expanded environment validation in src/config/env.validation.ts to include SENTRY_DSN, SENTRY_ENVIRONMENT, SENTRY_RELEASE, and SENTRY_TRACES_SAMPLE_RATE.
• Added Sentry configuration examples to .env.example and .env.production.example.
• Documented the Sentry configuration in README.md.
• Added @sentry/node to package.json.

Files changed

• src/config/sentry.ts
• src/common/middleware/sentry.middleware.ts
• src/main.ts
• src/common/filters/global-exception.filter.ts
• src/config/env.validation.ts
• .env.example
• .env.production.example
• README.md
• package.json

Environment variables added

• SENTRY_DSN
• SENTRY_ENVIRONMENT
• SENTRY_RELEASE
• SENTRY_TRACES_SAMPLE_RATE

Notes for reviewers

• Sentry initialization is intentionally skipped when SENTRY_DSN is not set.
• The global exception filter sends 500, 401, and 403 errors to Sentry for alerting and grouping.
• Uncaught exceptions and unhandled promise rejections are flushed before process exit.

Testing

• Run npm install after package.json update.
• Start the app with a valid SENTRY_DSN and verify startup logs include Sentry initialized.
• Trigger a handled error through a controller and confirm the event appears in Sentry.
• Trigger an uncaught exception to verify the process flushes Sentry events before exit.