Add mail-client keyboard shortcuts to inbox mine tab

j/k navigate up/down, a to archive, U to mark unread, r to mark read,
Enter to open. Includes server-side DELETE /issues/:id/read endpoint
for mark-unread support on issues.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

ui/src/api/issues.ts

@@ -53,6 +53,7 @@ export const issuesApi = {
   deleteLabel: (id: string) => api.delete<IssueLabel>(`/labels/${id}`),
   get: (id: string) => api.get<Issue>(`/issues/${id}`),
   markRead: (id: string) => api.post<{ id: string; lastReadAt: Date }>(`/issues/${id}/read`, {}),
+  markUnread: (id: string) => api.delete<{ id: string; removed: boolean }>(`/issues/${id}/read`),
   archiveFromInbox: (id: string) =>
     api.post<{ id: string; archivedAt: Date }>(`/issues/${id}/inbox-archive`, {}),
   unarchiveFromInbox: (id: string) =>