docs: move ACP checklist into packages/acp

Co-locate the ACP feature support checklist with the bridge package
(packages/acp/acp-feature-support.md) and rewrite its relative links for
the new depth. Broaden the doc-sync globs (doc-typecheck, verify-md-wrap,
verify-md-links) from packages/*/README.md to packages/*/*.md so a
package-level doc beyond the README stays under the drift gates, and
update the AGENTS.md prose describing that scope.

scripts/verify-md-links.ts

@@ -48,7 +48,7 @@ const root = resolve(import.meta.dirname, '..')
 const PATTERNS = [
   'README.md',
   'docs/**/*.md',
-  'packages/*/README.md',
+  'packages/*/*.md',
   'AGENTS.md',
   'packages/AGENTS.md',
   '.agents/skills/**/*.md',