feat(compose): add Docker Compose stack management

[dviejokfs]

Summary

• Adds a new Stacks feature for managing standalone Docker Compose stacks, separate from Temps projects
• New temps-compose crate with full three-layer architecture (handlers, services, entities)
• Frontend page with create/edit dialogs, YAML editor, and lifecycle controls (deploy, stop, restart)
• Lightweight Dockge/Portainer-style interface built directly into Temps — no extra tools needed

What's included

Backend

• temps-compose crate: service, handlers, plugin, error types, audit events
• compose_stacks database migration (id, name, description, compose_content, env_content, node_id, state)
• REST API: GET/POST /stacks, GET/PATCH/DELETE /stacks/{id}, POST /stacks/{id}/{deploy,stop,restart,pull}
• New permissions: StacksRead, StacksWrite, StacksDelete, StacksCreate (added to Admin, User, Reader roles)
• Audit logging for create, update, delete, and state change operations
• 8 unit tests

Frontend

• New "Stacks" sidebar item with Layers icon
• List view with state badges, responsive table
• Create dialog with YAML editor for compose content and .env variables
• Edit dialog for updating stack configuration
• Lifecycle dropdown: Deploy, Stop, Restart, Delete

Test plan

• cargo check --bin temps passes
• cargo test --lib -p temps-compose — 8 tests pass
• Clippy clean
• Manual test: create stack via API
• Manual test: verify frontend page renders
• Manual test: lifecycle operations (deploy/stop/restart)