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/infrastructure/src/lib/adapters/mappers.ts

@@ -98,5 +98,12 @@ export function toSettingsInput(
       name: a.name,
       archived: a.archived,
     })),
+    customFields: (settings.customFields ?? []).map((f) => ({
+      id: f.id,
+      name: f.name,
+      type: f.type,
+      options: f.options,
+      archived: f.archived,
+    })),
   };
 }