Publish structured apply progress events for Zi Setup #225

Problem

The Zi Setup client can report only coarse apply phases because public/sh/setup.sh publishes the final result after each phase but no machine-readable operation transitions.

Scope

Add an optional apply --events DIR contract that publishes versioned, ordered, atomic event artifacts for operation transitions. Document and test the contract, preserve existing behavior when the option is omitted, and regenerate public/checksum.txt.

The event contract must not require clients to parse human stdout or stderr. Event text must use the same bounded and safely encoded artifact conventions as the existing describe, plan, and result contracts.

Acceptance criteria

• Existing callers without --events are unchanged.
• Events identify phase, operation, status, and bounded detail.
• Clients can safely read each event while apply is still running.
• Success and failure paths publish chronological transitions.
• Installer and contract tests pass.