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>

apps/mcp/src/app/tools/summaries.ts

@@ -27,6 +27,7 @@ export const issueLine = (issue: Issue) => ({
   votes: issue.votes,
   storyPoints: issue.storyPoints,
   dueDate: issue.dueDate,
+  customFields: issue.customFields,
   labels: issue.labels,
   updatedAt: issue.updatedAt,
 });