refactor(cleanup): simplify pass on the R-a diff

engine-compare imports the coordinator's title limit and trim instead
of a copy whose reason went with Arm B; the autonomy gate exports one
parser and its test runs in-process with two CLI runs; one import
scanner in lib-imports; the fenced-section walker shared from
tests/helpers/md-section.mjs instead of six copies; plan-gate hash
in-process; living-paths scans once; routing drops the orchestrator
filter whose files are gone; small leftovers removed.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/review/coordinator-contract.mjs

@@ -444,7 +444,7 @@ function effectiveSeverity(f) {
   return getRule(f.rule_key)?.severity ?? f.severity;
 }
 
-function trimText(text, max) {
+export function trimText(text, max) {
   return text.slice(0, max - TRIM_MARKER.length) + TRIM_MARKER;
 }