feat: add Prettier for code formatting

Adds .prettierrc with Tailwind CSS plugin, .prettierignore, and format scripts.

Closes #27

Author: Ai-chan-0411

.prettierignore

@@ -0,0 +1,6 @@
+node_modules
+.next
+out
+build
+coverage
+pnpm-lock.yaml

.prettierrc

@@ -0,0 +1,11 @@
+{
+  "semi": true,
+  "singleQuote": false,
+  "tabWidth": 2,
+  "trailingComma": "all",
+  "printWidth": 80,
+  "bracketSpacing": true,
+  "arrowParens": "always",
+  "endOfLine": "lf",
+  "plugins": ["prettier-plugin-tailwindcss"]
+}

package.json

@@ -6,7 +6,9 @@
     "dev": "next dev",
     "build": "next build",
     "start": "next start",
-    "lint": "next lint"
+    "lint": "next lint",
+    "format": "prettier --write .",
+    "format:check": "prettier --check ."
   },
   "dependencies": {
     "@octokit/graphql": "^9.0.3",
@@ -30,6 +32,8 @@
     "eslint-config-next": "^16.2.2",
     "postcss": "^8.4.47",
     "tailwindcss": "^3.4.14",
+    "prettier": "^3.4.2",
+    "prettier-plugin-tailwindcss": "^0.6.11",
     "typescript": "^6.0.2"
   }
 }