🤖 Add orbit prototype plugin for Rust code review

Standalone plugin with one skill: when to use orbit and when grep, a
mandatory preflight for stale indexes and blind regions (cfg(test),
features, macros, dyn dispatch), a scripted review pass over isolated
worktree DBs, and a JSONL feedback log for mining real usage later.
Registered in the marketplace as a prototype.

.claude-plugin/marketplace.json

@@ -34,6 +34,11 @@
       "name": "gitea",
       "source": "./plugins/gitea",
       "description": "Bidirectional Gitea ticket integration: fetch context, create issues, post comments, list/search, close, and scaffold labels"
+    },
+    {
+      "name": "orbit",
+      "source": "./plugins/orbit",
+      "description": "PROTOTYPE — orbit code-graph skill for reviewing Rust changes: blast radius, trait-impl coverage, crate boundaries, cfg-blindness preflight. Needs the orbit CLI."
     }
   ]
 }