hold coverage_floor fixed at 90

Stop ratcheting the pre-push line-coverage floor. 90% is the standing
obligation; gains above it are welcome but no longer raise the gate.

Co-Authored-By: Claude <noreply@anthropic.com>

pubspec.yaml

@@ -16,9 +16,9 @@ publish_to: none
 version: 2.0.0
 repository: https://github.com/postmeridiem/clide
 
-# Pre-push line-coverage floor. Ratchets up only — see D-66.
+# Pre-push line-coverage floor. Held fixed at 90 — see D-66.
 # Reading: `awk -F: '/^coverage_floor:/ {gsub(/ /,"",$2); print $2}' pubspec.yaml`.
-coverage_floor: 92
+coverage_floor: 90
 
 # Project metadata (was project.yaml, folded in per D-056).
 # version: above is the single source of truth. The Makefile reads