fix: remove duplicate hooks declaration from plugin.json

Fixes #103, #106, #108

Claude Code automatically loads hooks/hooks.json by convention.
Explicitly declaring it in plugin.json causes a duplicate detection
error: "Duplicate hooks file detected"

Added regression test to prevent this from being reintroduced.

.claude-plugin/plugin.json

@@ -38,6 +38,5 @@
     "./agents/refactor-cleaner.md",
     "./agents/security-reviewer.md",
     "./agents/tdd-guide.md"
-  ],
-  "hooks": "./hooks/hooks.json"
+  ]
 }