feat: add ActualBudget app

[sylvainmetayer]

Summary

• Scaffold the actualbudget Ansible role (compose, borgmatic backup, docker.yml wiring) based on the official Docker install instructions (https://actualbudget.org/docs/install/docker)
• Add Pangolin routing/SSO/healthcheck + backup-push monitor via Tofu (budget.sylvain.cloud)
• Wire actualbudget into the backup folder list and host_vars

Closes #63

Test plan

• ansible-lint roles/actualbudget passes
• ansible-playbook docker.yml --syntax-check passes
• tofu fmt -recursive && tofu validate pass in tofu/pangolin_config
• tofu plan shows the expected actualbudget resources being created
• tofu apply then ansible-playbook -i inventory/hosts docker.yml --tags actualbudget,app (not run — nothing was applied/deployed as requested)
• Verify https://budget.sylvain.cloud loads and Uptime Kuma healthcheck/backup-push monitors go green after apply

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