Diagnostic for durable subscriptions without an explicit name #847

Problem

EventBus.subscribe_durable(event, handler) without name= keys outbox rows by the handler's import path (simple_module_core/durable_events.py handler_name). Moving or renaming the handler module silently strands every undelivered row: it retries as an unknown handler, then goes dead. The module-layout moves hit exactly this (fixed before release in #843).

host/tests/test_durable_wire_names.py now freezes the names in this repo, but downstream modules get no warning.

Proposal

Add a diagnostic (next free SM0xx), run by make doctor and a dev boot, that reports a subscribe_durable call without an explicit name= (a warning, with the fix: pass a constant from constants.py). Pin the remaining in-repo default names (permissions, tenants user cleanup) to constants when those modules move. Document it in docs/framework/events.md and docs/reference/diagnostic-codes.md.