Require explicit devices subcommand

[upsetbit]

Closes #104.

Summary

• remove the prosa devices parent default that ran devices list
• keep devices list as the explicit command
• add a regression test that devices and schedule parents both render subcommand usage

Local validation

• go test ./internal/cli/... -run 'TestParentCommandsRequireExplicitSubcommands|TestNoColor|TestApplyGlobal' -count=1 -v\n- go test ./internal/cli/... -race\n- devbox run -- just lint\n- just test-race

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