Hot-reloadable runtime parameters — Tier 2: live concurrency, correctness-coupled cadences, Python/UI parity (#385)

## Summary

Tier 2 of #385 (ADR-038): the hot-reload knobs that need structural work beyond the Tier 1 override columns.

- **Live concurrency** — `max_workers` / `min_workers` changes require resizing the permit pool at runtime and interact with weighted-overflow accounting; needs a design pass on in-flight-permit semantics during shrink.
- **Cadence knobs coupled to correctness** — `heartbeat_interval`, `heartbeat_staleness`, rescue intervals: changing these live interacts with crash-recovery guarantees (a worker whose staleness shrank under a long-running fleet could rescue healthy peers); needs the same closed-under-transitions style analysis the unique-states masks got.
- **Python admin parity + UI editing** for the Tier 1 surface.

Blocked on the Tier 1 issue's override plumbing landing first.

Start with ADR-038 and the Tier 1 issue #385, since this work is explicitly blocked on its override plumbing. Analyze live permit-pool resizing and cadence transitions for in-flight and crash-recovery correctness, then cover the stated Python admin and UI parity; done means the design questions are resolved and the Tier 2 surface is implemented.

Written by the indexing model from the issue text.