fix: add missing agents and hooks declarations to plugin.json

- Added agents field pointing to ./agents directory (10 agents)
- Added hooks field pointing to ./hooks/hooks.json
- These were supported but not declared, potentially causing
  agents not to load when installed as a plugin

Addresses part of #88 (rules still need manual install per
upstream limitation - filed anthropics/claude-code#21163)

.claude-plugin/plugin.json

@@ -23,5 +23,7 @@
     "best-practices"
   ],
   "commands": "./commands",
-  "skills": "./skills"
+  "skills": "./skills",
+  "agents": "./agents",
+  "hooks": "./hooks/hooks.json"
 }