fix: romaji index routes moved after app init + kuromoji in root package.json

- app.get/delete for /api/romaji-index were placed before const app = express()
  causing ReferenceError on startup — moved into the ROUTES section
- kuromoji moved from backend/package.json to root package.json so Docker
  picks it up during the existing npm install step
- Fixed dicPath resolution to use path.dirname(require.resolve(...))

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

package.json

@@ -7,6 +7,9 @@
     "preview": "vite preview",
     "icons": "node scripts/gen-icons.mjs"
   },
+  "dependencies": {
+    "kuromoji": "^0.1.2"
+  },
   "devDependencies": {
     "sharp": "^0.34.5",
     "vite": "^5.4.0"