feat(claude): bump latest=2.1.120 + verify ae2/ae3 markers in installer

- index.json latest: 2.1.119 → 2.1.120 (artifacts already published in
  releases/v2.1.120/sea/, manifest carries ae3 patched binary sha256
  eb126100...)
- uclaude_install.sh SEA verification expanded: now requires ae1 + ae2 +
  ae3 + bypass markers (was only ae1 + bypass). ae2 gates the /model
  picker for custom-prefixed models, ae3 gates Agent.model accepting
  gpt-5.5/glm-5.1 — both critical for the proxy workflow.

After this: new machines doing
  curl ... uclaude_install.sh | sudo bash
get v2.1.120 directly with all 9 patches; verification step catches
any missing patch with explicit "missing: ae3" diagnostic.

claude/releases/index.json

@@ -1,6 +1,13 @@
 {
-  "latest": "2.1.119",
+  "latest": "2.1.120",
   "releases": [
+    {
+      "version": "2.1.120",
+      "date": "2026-04-26",
+      "patches": 9,
+      "status": "stable",
+      "install_type": "sea_binary"
+    },
     {
       "version": "2.1.119",
       "date": "2026-04-24",