feat: custom fields per project

Text, number, date or option-list fields defined in the project settings
(archived, never removed; their type is fixed once saved). Tickets hold
them, edited in the side panel, listed under the title and filtered by
option in the list view; also over GraphQL, REST (?field=ID:value) and MCP.

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

libs/web/tracker/domain/src/lib/models/models.ts

@@ -7,7 +7,7 @@ import {
   SprintStatus,
   StatusCategory,
 } from './enums';
-import { ProjectSettings } from './workflow';
+import { CustomFieldValue, ProjectSettings } from './workflow';
 
 export interface UserRef {
   id: string;
@@ -126,6 +126,8 @@ export interface IssueSummary {
   /** Planned start and end (`YYYY-MM-DD`), for the roadmap. */
   startDate: string | null;
   dueDate: string | null;
+  /** Values of the project's custom fields (only those set). */
+  customFields: CustomFieldValue[];
   /** In the trash since then (null: not in it). */
   trashedAt: string | null;
   commentCount: number;