fix: sync plugin.json version with package.json

Bump .claude-plugin/plugin.json from 1.0.0 to 1.4.0 and add an npm
version lifecycle script to keep them in sync automatically.

.claude-plugin/plugin.json

@@ -1,6 +1,6 @@
 {
   "name": "apple-mail",
-  "version": "1.0.0",
+  "version": "1.4.0",
   "description": "Manage Apple Mail through natural language - read, search, send, and organize emails (macOS only)",
   "author": {
     "name": "Rob Sweet",

package.json

@@ -27,6 +27,7 @@
     "format": "prettier --write src",
     "format:check": "prettier --check src",
     "typecheck": "tsc --noEmit",
+    "version": "node -e \"const p=require('./package.json'); const f='.claude-plugin/plugin.json'; const c=JSON.parse(require('fs').readFileSync(f,'utf8')); c.version=p.version; require('fs').writeFileSync(f,JSON.stringify(c,null,2)+'\\n')\" && git add .claude-plugin/plugin.json",
     "prepublishOnly": "npm run lint && npm run test && npm run build",
     "prepare": "husky && npm run build"
   },