search: Phase 4 federation merge + ACL post-filter + 21 tests

fedIndex merges per-peer inverted indices (union posting lists per term) after
relabelling local DocIds to global gid = peer*1000 + local — dedupe by
(peer,doc-id) is automatic and positions survive, so ranking runs once over the
merge and interleaves peers by score. ACL is a post-rank filter over an injected
permit predicate (searchTfIdfAcl/topNTfIdfAcl/searchBm25Acl). Roadmap complete,
122/122.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/search/scoreboard.json

@@ -1,13 +1,14 @@
 {
   "lang": "search",
-  "total_passed": 101,
+  "total_passed": 122,
   "total_failed": 0,
-  "total": 101,
+  "total": 122,
   "suites": [
     {"name":"index","passed":18,"failed":0,"total":18},
     {"name":"boolean","passed":28,"failed":0,"total":28},
     {"name":"parse","passed":32,"failed":0,"total":32},
-    {"name":"rank","passed":23,"failed":0,"total":23}
+    {"name":"rank","passed":23,"failed":0,"total":23},
+    {"name":"integration","passed":21,"failed":0,"total":21}
   ],
-  "generated": "2026-06-06T19:56:08+00:00"
+  "generated": "2026-06-06T20:07:30+00:00"
 }