feat: pinned tickets, at hand on the home page and in search

Each person pins up to 20 tickets from the ticket's page («Fijar»). They
show as a strip under the projects on the home page and in the search
palette before typing. Private and without history, like the views of
«my work» (Mongo `pinned_issues`); tickets in the trash or out of reach
are left out, and when the list is full the unreadable ones are dropped
first.

API: GET /api/me/pins, PUT/DELETE /api/issues/{issue}/pin; GraphQL
myPins, pinIssue, unpinIssue and Issue.pinned.

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

libs/web/tracker/infrastructure/src/lib/graphql/fragments.graphql

@@ -120,6 +120,7 @@ fragment IssueSummaryFields on Issue {
 
 fragment IssueFields on Issue {
   ...IssueSummaryFields
+  pinned
   description
   figmaUrl
   createdAt