Say beta in the label the plugin picker shows

While the major version is 0 the command surface can still move, and until
now the only places that said so were the README and the changelog — neither of
which a user reads before installing.

displayName is the label the /plugin picker shows. It is UI-only: it never
affects the command namespace, the install id, or an enabledPlugins key, so the
marker costs nothing mechanical and comes off again in the same commit that
declares 1.0.0.

Author: durchnull

.claude-plugin/plugin.json

@@ -1,5 +1,6 @@
 {
   "name": "git",
+  "displayName": "Git (Beta)",
   "description": "Branch-flow git workflow for a protected promotion chain, configured per project: commit + push + open a PR (ship, with --split for focused PRs), cut a promotion PR to the pre-production tier (promote), and cut a release PR to production then tag it (release). Run init once to teach it the repo's branch flow and quality gates.",
   "version": "0.1.0",
   "author": {