Feature: Sentry Integration for Observability

[JudahSan]

Goal
Add Sentry for error + performance monitoring via Rails credentials.

Tasks

• Configure DSN + enabled flag in credentials
• Add smart sampling & scrub sensitive data
• Link releases to git commits
• Ensure safe behavior in dev/test

Test
Update config/credentials/development.yml.enc with creds, then verify per Sentry Rails docs.