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/gardens.ts

@@ -0,0 +1,49 @@
+import client from './client'
+
+export interface Garden {
+  id?: number
+  nom: string
+  description?: string
+  type: string
+  latitude?: number
+  longitude?: number
+  adresse?: string
+  exposition?: string
+  ombre?: string
+  sol_type?: string
+  grille_largeur: number
+  grille_hauteur: number
+}
+
+export interface GardenCell {
+  id?: number
+  garden_id?: number
+  col: number
+  row: number
+  libelle?: string
+  etat: string
+  notes?: string
+}
+
+export interface Measurement {
+  id?: number
+  garden_id?: number
+  temp_air?: number
+  temp_sol?: number
+  humidite_air?: number
+  humidite_sol?: number
+  source?: string
+  ts?: string
+}
+
+export const gardensApi = {
+  list: () => client.get<Garden[]>('/api/gardens').then(r => r.data),
+  get: (id: number) => client.get<Garden>(`/api/gardens/${id}`).then(r => r.data),
+  create: (g: Partial<Garden>) => client.post<Garden>('/api/gardens', g).then(r => r.data),
+  update: (id: number, g: Partial<Garden>) => client.put<Garden>(`/api/gardens/${id}`, g).then(r => r.data),
+  delete: (id: number) => client.delete(`/api/gardens/${id}`),
+  cells: (id: number) => client.get<GardenCell[]>(`/api/gardens/${id}/cells`).then(r => r.data),
+  measurements: (id: number) => client.get<Measurement[]>(`/api/gardens/${id}/measurements`).then(r => r.data),
+  addMeasurement: (id: number, m: Partial<Measurement>) =>
+    client.post<Measurement>(`/api/gardens/${id}/measurements`, m).then(r => r.data),
+}