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/api/tracker/presenters/src/lib/graphql/issue.resolver.ts

@@ -43,6 +43,7 @@ import {
   CommandResultGql,
   CommentPageGql,
   EpicGql,
+  CustomFieldValueGql,
   IssueGql,
   IssuePageGql,
   IssueParentGql,
@@ -75,8 +76,10 @@ export class IssueResolver {
     @Args('limit', { type: () => Int, defaultValue: 50 }) limit: number,
     @Args('offset', { type: () => Int, defaultValue: 0 }) offset: number,
   ) {
+    const { customFields, ...rest } = filter;
     return this.issuesService.search(viewerOf(me), {
-      ...filter,
+      ...rest,
+      customFields: onlyValues(customFields),
       limit,
       offset,
     });
@@ -150,6 +153,16 @@ export class IssueResolver {
     });
   }
 
+  @ResolveField(() => [CustomFieldValueGql], {
+    description: "Values of the project's custom fields (only those set)",
+  })
+  customFields(@Parent() issue: IssueReadModel): CustomFieldValueGql[] {
+    return Object.entries(issue.customFields ?? {}).map(([fieldId, value]) => ({
+      fieldId,
+      value,
+    }));
+  }
+
   @ResolveField(() => [String], {
     description: "Statuses this ticket can move to next (project's workflow)",
   })
@@ -432,3 +445,13 @@ export class IssueResolver {
     return this.issuesService.setRelease(me.id, issueId, releaseId ?? null);
   }
 }
+
+/** A filter's custom values: the ones that name something to match. */
+function onlyValues(
+  values: { fieldId: string; value?: string | null }[] | undefined,
+): Record<string, string> | undefined {
+  const pairs = (values ?? []).filter((v) => v.value);
+  return pairs.length
+    ? Object.fromEntries(pairs.map((v) => [v.fieldId, v.value as string]))
+    : undefined;
+}