Per-service settings pages

Each service now has its own settings page, so you no longer edit chart values by hand.

• Trino: workers, memory and catalogs.
• Prometheus and Alertmanager: retention, scrape targets and notifications.
• Grafana: extra data sources.
• MinIO: buckets and users with a policy.
• Airflow: executor and DAGs from Git.

Every change is validated, shown for review with what will restart, written to your Git repository and reconciled by Flux. Passwords and webhook URLs go to Vault and never into Git.