Add frontend API client and TanStack Query hooks

Install @tanstack/react-query, create a fetch-based API client with typed
functions for all endpoints, and add query/mutation hooks for games, pokemon,
runs, and encounters. Includes Vite dev proxy for /api and QueryClientProvider
setup.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/hooks/useEncounters.ts

@@ -0,0 +1,43 @@
+import { useMutation, useQueryClient } from '@tanstack/react-query'
+import {
+  createEncounter,
+  updateEncounter,
+  deleteEncounter,
+} from '../api/encounters'
+import type { CreateEncounterInput, UpdateEncounterInput } from '../types/game'
+
+export function useCreateEncounter(runId: number) {
+  const queryClient = useQueryClient()
+  return useMutation({
+    mutationFn: (data: CreateEncounterInput) => createEncounter(runId, data),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['runs', runId] })
+    },
+  })
+}
+
+export function useUpdateEncounter(runId: number) {
+  const queryClient = useQueryClient()
+  return useMutation({
+    mutationFn: ({
+      id,
+      data,
+    }: {
+      id: number
+      data: UpdateEncounterInput
+    }) => updateEncounter(id, data),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['runs', runId] })
+    },
+  })
+}
+
+export function useDeleteEncounter(runId: number) {
+  const queryClient = useQueryClient()
+  return useMutation({
+    mutationFn: (id: number) => deleteEncounter(id),
+    onSuccess: () => {
+      queryClient.invalidateQueries({ queryKey: ['runs', runId] })
+    },
+  })
+}