fix(cli): emit json for profile mutations

[upsetbit]

Summary

Fixes #295.

profiles add, profiles set-path, and profiles remove now emit JSON when the inherited --json flag is present.

What changed

• Added a machine-readable mutation payload for profile changes.
• add emits action, agent, profile, path, and replaced when applicable.
• set-path emits action, agent, profile, and path.
• remove emits action, agent, and profile.
• Added command-level tests with temporary profile config.

Validation

• go test ./internal/cli -run 'TestProfilesMutatorsEmitJSON' -count=1
• go test ./internal/cli/... -race
• go build -o ./bin/prosa ./cmd/prosa
• Manual checks for add/set-path/remove with --json piped through python3 -m json.tool