chore: update Go version to 1.26 and refactor logging

[abhimanyu003]

Summary

• Bump Go to 1.26 in go.mod, the Dockerfile and the build workflow
• Update dependencies (echo v4.16.0, amqp091-go v1.15.0, x/* libs)
• Replace stdlib log with charm.land/log/v2 for leveled, structured logs

Notes

• Log lines now have a level and key=value fields, e.g. INFO connecting to RabbitMQ host=... port=.... Update any alerts that match the old log text.
• Timestamps, stderr output and fatal exit codes are the same as before.