chore(omo): vendor impeccable skill 4.6.0

Re-copy .opencode/skills/impeccable from upstream tag skill-v4.6.0
(8a0e198, engine 0.1.15), keep LICENSE, and re-apply the OmO path
rewrite and the critique routing line.

The documented rewrite missed the base-directory fallback in SKILL.md,
which ends at scripts rather than scripts/impeccable, so the upgrade
command now rewrites the scripts directory prefix. The skills README
also notes that the engine binary is downloaded by scripts/VERSION
rather than vendored.

.config/omo/skills/impeccable/scripts/live-browser-session.js

@@ -44,6 +44,10 @@
 
     function saveSession(session) {
       if (!session || !session.id) return;
+      // Adopt a revision another tab stored so this write does not lower it.
+      // localStorage has no compare-and-set, so a save from another tab that
+      // lands between this read and the write below can still be overwritten.
+      loadSession();
       const payload = {
         ...session,
         checkpointRevision,
@@ -56,8 +60,8 @@
     }
 
     function nextCheckpointRevision() {
-      checkpointRevision += 1;
       const existing = loadSession();
+      checkpointRevision += 1;
       if (existing?.id) saveSession(existing);
       return checkpointRevision;
     }