[Feature]: Adopt structured logging (log/slog) for all user-facing output

[mrhillsman]

Problem Statement

All user-facing output uses `fmt.Printf` where structured logging (`log/slog`) would be more appropriate. This affects observability when running in containerized/OpenShift environments where structured JSON logs are expected by log aggregation systems.

Proposed Solution

Adopt `log/slog` (stdlib, available since Go 1.21) with configurable log level via `--verbose` flag. Use structured fields for VM names, namespaces, durations, and error details.

Alternatives Considered

Not provided

Area

CLI / Configuration

Additional Context

Severity: Medium

Files with `fmt.Print` in non-test code:*

• `cmd/virtwork/main.go` — ~15 `fmt.Fprintf` calls for status, errors, and summary output
• `internal/wait/wait.go:38` — `fmt.Printf` for retry messages
• `internal/vm/vm.go` — `fmt.Printf` for retry backoff messages