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/plantings.ts

@@ -0,0 +1,31 @@
+import client from './client'
+
+export interface Planting {
+  id?: number
+  garden_id: number
+  variety_id: number
+  cell_id?: number
+  date_plantation?: string
+  quantite: number
+  statut: string
+  notes?: string
+}
+
+export interface PlantingEvent {
+  id?: number
+  planting_id?: number
+  type: string
+  note?: string
+  ts?: string
+}
+
+export const plantingsApi = {
+  list: () => client.get<Planting[]>('/api/plantings').then(r => r.data),
+  get: (id: number) => client.get<Planting>(`/api/plantings/${id}`).then(r => r.data),
+  create: (p: Partial<Planting>) => client.post<Planting>('/api/plantings', p).then(r => r.data),
+  update: (id: number, p: Partial<Planting>) => client.put<Planting>(`/api/plantings/${id}`, p).then(r => r.data),
+  delete: (id: number) => client.delete(`/api/plantings/${id}`),
+  events: (id: number) => client.get<PlantingEvent[]>(`/api/plantings/${id}/events`).then(r => r.data),
+  addEvent: (id: number, e: Partial<PlantingEvent>) =>
+    client.post<PlantingEvent>(`/api/plantings/${id}/events`, e).then(r => r.data),
+}