feat(tickets): ajoute les pièces jointes sur tickets (#108)

Stockage flat côté ticket + métadonnées d'attachments, lecture exposée côté
backend/MCP, et UI minimale de liste/ajout dans TicketDetail. Traverse le
domaine (Issue, ports), l'application (usecases + assistant de ticket), les
adaptateurs infra/MCP (issues store, orchestrateur), les DTO backend/web-
server/app-tauri, et le frontend (domain/ports/adapters/hooks/UI).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/ports/index.ts

@@ -68,6 +68,7 @@ import type {
   TerminalSession,
   Ticket,
   TicketBulkResult,
+  TicketAttachmentContent,
   TicketChat,
   TicketCarnet,
   TicketLinkKind,
@@ -96,6 +97,12 @@ export interface SystemGateway {
    * cancelled. Same sanctioned-picker rule as {@link pickFolder}.
    */
   pickArchiveFile(): Promise<string | null>;
+  /**
+   * Opens a native file picker for one local file and returns its path, or
+   * `null` when cancelled. Used for ticket attachments; no file bytes cross the
+   * frontend boundary.
+   */
+  pickFile(): Promise<string | null>;
   /**
    * Subscribes to the app-exit work-in-progress guard (ticket #83): fired when
    * closing the main window is intercepted because it would interrupt active
@@ -1096,6 +1103,27 @@ export interface TicketGateway {
     carnet: string,
     expectedVersion: number,
   ): Promise<Ticket>;
+  /** Adds a local file path as a ticket attachment and returns the updated ticket. */
+  addAttachment(
+    projectId: string,
+    ref: string,
+    path: string,
+    expectedVersion: number,
+    mime?: string | null,
+  ): Promise<Ticket>;
+  /** Reads raw attachment content as base64. Not used by the minimal v1 UI. */
+  readAttachment(
+    projectId: string,
+    ref: string,
+    attachmentId: string,
+  ): Promise<TicketAttachmentContent>;
+  /** Marks an attachment as summarized in the ticket carnet. */
+  markAttachmentSummarized(
+    projectId: string,
+    ref: string,
+    attachmentId: string,
+    expectedVersion: number,
+  ): Promise<Ticket>;
   /** Links this ticket to another `#id` with the given relationship kind. */
   link(
     projectId: string,