Add pre-commit hooks for linting and formatting

Set up pre-commit framework with ruff (backend) and ESLint/Prettier/tsc
(frontend) hooks to catch issues locally before CI. Auto-format all
frontend files with Prettier to comply with the new check.

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

frontend/src/utils/download.ts

@@ -1,5 +1,7 @@
 export function downloadJson(data: unknown, filename: string) {
-  const blob = new Blob([JSON.stringify(data, null, 2)], { type: 'application/json' })
+  const blob = new Blob([JSON.stringify(data, null, 2)], {
+    type: 'application/json',
+  })
   const url = URL.createObjectURL(blob)
   const a = document.createElement('a')
   a.href = url

frontend/src/utils/formatEvolution.ts

@@ -1,18 +1,30 @@
-export function formatEvolutionMethod(evo: { trigger: string; minLevel: number | null; item: string | null; heldItem: string | null; condition: string | null }): string {
+export function formatEvolutionMethod(evo: {
+  trigger: string
+  minLevel: number | null
+  item: string | null
+  heldItem: string | null
+  condition: string | null
+}): string {
   const parts: string[] = []
   if (evo.trigger === 'level-up' && evo.minLevel) {
     parts.push(`Level ${evo.minLevel}`)
   } else if (evo.trigger === 'level-up') {
     parts.push('Level up')
   } else if (evo.trigger === 'use-item' && evo.item) {
-    parts.push(evo.item.replace(/-/g, ' ').replace(/\b\w/g, c => c.toUpperCase()))
+    parts.push(
+      evo.item.replace(/-/g, ' ').replace(/\b\w/g, (c) => c.toUpperCase())
+    )
   } else if (evo.trigger === 'trade') {
     parts.push('Trade')
   } else {
-    parts.push(evo.trigger.replace(/-/g, ' ').replace(/\b\w/g, c => c.toUpperCase()))
+    parts.push(
+      evo.trigger.replace(/-/g, ' ').replace(/\b\w/g, (c) => c.toUpperCase())
+    )
   }
   if (evo.heldItem) {
-    parts.push(`holding ${evo.heldItem.replace(/-/g, ' ').replace(/\b\w/g, c => c.toUpperCase())}`)
+    parts.push(
+      `holding ${evo.heldItem.replace(/-/g, ' ').replace(/\b\w/g, (c) => c.toUpperCase())}`
+    )
   }
   if (evo.condition) {
     parts.push(evo.condition)