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/http/issues.controller.ts

@@ -171,6 +171,14 @@ export class IssuesController {
       watching: query.watching,
       dueFrom: query.dueFrom,
       dueTo: query.dueTo,
+      customFields: query.field?.length
+        ? Object.fromEntries(
+            query.field.map((f) => [
+              f.slice(0, f.indexOf(':')),
+              f.slice(f.indexOf(':') + 1),
+            ]),
+          )
+        : undefined,
       sort: query.sort,
       search: query.search,
       limit: query.limit,