Add missing "play" script to package.json

Adds a "play" script as an alias for "start" (both run `node dist/index.js`).
This resolves confusion where users might try `npm run play` based on the
bot's music-playing nature.

Fixes #11

https://claude.ai/code/session_01GC6qsKsmiroNkruLENDhPq

package.json

@@ -8,6 +8,7 @@
     "build": "tsc && npm run build:web",
     "build:web": "cd web && npm run build",
     "start": "node dist/index.js",
+    "play": "node dist/index.js",
     "test": "vitest run",
     "test:watch": "vitest"
   },