perf: make DORA metric commands async (#309)

[sauravpanda]

Summary

• Made record_deployment, get_dora_metrics, and list_deployments Tauri commands async to avoid blocking the main IPC thread with synchronous SQLite queries
• Follows the existing pattern used by other async commands in the codebase (e.g., export_backup, stop_process)

Closes #309

Test plan

• cargo clippy -- -D warnings passes
• All 168 unit tests pass (cargo test)