Import bénévoles : couche API (analyse + exécution) et mock CSV

- `PlanningApi.imports.analyze/execute` : envoi `multipart/form-data`
  (le client HTTP laisse le navigateur poser le Content-Type).
- Types miroir des schémas back-end (`ImportAnalyzeResponse`,
  `ImportMapping`, `ImportReport`, `ImportRowReport`, `ImportIssue`…).
- Hooks `useAnalyzeImport` / `useExecuteImport` ; l'exécution réelle
  invalide les bénévoles et le planning.
- Implémentation mock (mode démo) : lecture CSV, suggestion de mapping,
  simulation/exécution avec rapport ligne par ligne. Excel renvoie
  `import.error.xlsx_demo_only`.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017uUsRg7XzopkCPWimwg9ZM

frontend/src/api/schema.ts

@@ -135,6 +135,96 @@ export interface VolunteerUpdate {
   skill_codes?: string[] | null;
 }
 
+// --------------------------------------------------------------------------- //
+// Import de bénévoles (fichier CSV / Excel)                                    //
+// --------------------------------------------------------------------------- //
+export type ImportFieldKey =
+  | 'first_name'
+  | 'last_name'
+  | 'email'
+  | 'phone'
+  | 'tshirt_size'
+  | 'diet'
+  | 'comment'
+  | 'skills';
+
+export interface ImportColumnMapping {
+  first_name: string;
+  last_name: string;
+  email?: string | null;
+  phone?: string | null;
+  tshirt_size?: string | null;
+  diet?: string | null;
+  comment?: string | null;
+  skills?: string | null;
+}
+
+export interface ImportAvailabilityColumn {
+  header: string;
+  /** Date ISO (YYYY-MM-DD). */
+  date: string;
+  day_part_code: string;
+}
+
+export interface ImportMapping {
+  dry_run: boolean;
+  columns: ImportColumnMapping;
+  availability_columns: ImportAvailabilityColumn[];
+}
+
+export interface ImportPreviewRow {
+  line: number;
+  values: Record<string, string>;
+}
+
+export interface ImportDayPartInfo {
+  code: string;
+  label: string;
+  start_time: string;
+  end_time: string;
+  order: number;
+}
+
+export interface ImportAnalyzeResponse {
+  filename: string;
+  format: 'csv' | 'xlsx';
+  headers: string[];
+  row_count: number;
+  preview: ImportPreviewRow[];
+  suggested_mapping: Partial<Record<ImportFieldKey, string>>;
+  /** Dates ISO couvertes par l'édition. */
+  edition_dates: string[];
+  day_parts: ImportDayPartInfo[];
+}
+
+export type ImportSeverity = 'ERROR' | 'WARNING';
+export type ImportRowAction = 'CREATED' | 'UPDATED' | 'SKIPPED';
+
+export interface ImportIssue {
+  code: string;
+  severity: ImportSeverity;
+  field?: string | null;
+  params: Record<string, string | number | null>;
+}
+
+export interface ImportRowReport {
+  line: number;
+  action: ImportRowAction;
+  volunteer_id: string | null;
+  issues: ImportIssue[];
+}
+
+export interface ImportReport {
+  dry_run: boolean;
+  total_rows: number;
+  created: number;
+  updated: number;
+  skipped: number;
+  availabilities_written: number;
+  skills_created: string[];
+  rows: ImportRowReport[];
+}
+
 // --------------------------------------------------------------------------- //
 // Position                                                                     //
 // --------------------------------------------------------------------------- //