Runlet 0.6.0

Runlet 0.6.0

Includes #2 (merged as 84fb4f8):

• Adds Runtime::run_with_progress and a bounded, nonblocking, payload-free progress channel with source spans, run-local node IDs, typed states, relationships, sequence numbers, and terminal outcomes.
• Makes lifecycle reporting distinguish capacity waiting from real handler execution, preserves terminal-state ordering, and explicitly reports overflow or incomplete observation without stopping execution.
• Preserves nested retry attempt metadata and iteration/retry relationships. Existing execution and observation APIs remain available.

The Kit compose progress bridge is a separate integration and is not included in this crate release. The stream has no replay or live resynchronization after overflow.

No dependency upgrades.