docs(1.0-readiness): name the retired attribute without spelling it

The `no retired $apiPrefix` gate — added in 0.25.0 precisely because docs kept
teaching vocabulary the loader had retired — fired on the §G3 entry I had just
written, which named the attribute literally while listing what 0.25.0 broke.

Rephrased to "the API base URL leaves the entity descriptor", the CHANGELOG
heading's own wording, rather than widening the gate's exemption list. The
exemptions are for `docs/superpowers/`, the `docs/llms/` mirrors and the
migration guide — a dated record and a migration note must be able to name what
was retired. A readiness ledger does not need the literal token to make its
point, and every entry added to that list makes the gate weaker for the next
reader who does teach it by accident.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3v6M6uqECZ2Sb5eUv6YY

Author: dmealing

docs/1.0-readiness.md

@@ -216,7 +216,7 @@ Status legend: ✅ done · 🔶 in progress · ⬜ not started · ❓ **[RATIFY]
   all five ports, and TypeScript, C# and Python **loaded every one of those before**. So a
   document that loads on `0.24.x` stops loading, which is exactly the test the `0.24.2`
   ruling used to distinguish a resetting release from a quiet one. Five further breaking
-  changes ship beside it (`$apiPrefix` leaves the entity descriptor, a TPH subtype's `$path`,
+  changes ship beside it (the API base URL leaves the entity descriptor, a TPH subtype's `$path`,
   `<Entity>Names`' shape, the removed `@metaobjectsdev/sdk/agent-docs` subpath, Python's
   `GenConfig.column_naming`), and each forces adopter edits.