feat: bulk edit tickets

Select several tickets in the backlog and change their status, assignee,
sprint, priority or labels at once. Each ticket goes through the normal
rules and may refuse on its own; the result says which did.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/lib/ports/gateways.ts

@@ -41,6 +41,8 @@ import {
   UpdateIssueInput,
   UpdateProjectInput,
   CreateSprintInput,
+  BulkChange,
+  BulkResult,
   UpdateSprintInput,
 } from '../models/inputs';
 
@@ -113,6 +115,11 @@ export abstract class IssuesGateway {
     parentId: string | null,
   ): Observable<CommandResult>;
   abstract epics(projectId: string): Observable<Epic[]>;
+  /** The same change on several tickets; each may refuse on its own. */
+  abstract bulkUpdate(
+    issueIds: string[],
+    change: BulkChange,
+  ): Observable<BulkResult>;
   /** Tickets still to start (TODO category), in backlog order. */
   abstract backlog(projectId: string): Observable<IssuePage>;
   /** Moves a ticket between two others of the backlog (null: an end). */