fix: remove agents field from git-flow plugin.json

Claude Code doesn't support the agents field in plugin manifests.
Commands-only manifest should work.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

plugins/git-flow/.claude-plugin/plugin.json

@@ -16,6 +16,5 @@
     "branch",
     "automation"
   ],
-  "commands": ["./commands/"],
-  "agents": ["./agents/"]
+  "commands": ["./commands/"]
 }