feat(frontend): API layer + stores Pinia

Ajoute le client Axios, les modules API (gardens, varieties, plantings,
tasks) et les stores Pinia correspondants. Corrige tsconfig.json pour
inclure vite/client et DOM.Iterable.

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

frontend/src/api/varieties.ts

@@ -0,0 +1,23 @@
+import client from './client'
+
+export interface PlantVariety {
+  id?: number
+  nom_commun: string
+  nom_botanique?: string
+  variete?: string
+  famille?: string
+  type_plante?: string
+  besoin_eau?: string
+  espacement_cm?: number
+  plantation_mois?: string
+  recolte_mois?: string
+  notes?: string
+}
+
+export const varietiesApi = {
+  list: () => client.get<PlantVariety[]>('/api/varieties').then(r => r.data),
+  get: (id: number) => client.get<PlantVariety>(`/api/varieties/${id}`).then(r => r.data),
+  create: (v: Partial<PlantVariety>) => client.post<PlantVariety>('/api/varieties', v).then(r => r.data),
+  update: (id: number, v: Partial<PlantVariety>) => client.put<PlantVariety>(`/api/varieties/${id}`, v).then(r => r.data),
+  delete: (id: number) => client.delete(`/api/varieties/${id}`),
+}