- ticket-create.js: added 子服务器 dropdown (group/server from
/polls/server-list, supports anonymous users), sends 'server' field
- tickets.js POST: accept server param, resolve 'group/server' or
alias/server_name from server_groups, store into tickets.server_name
- polls.js: new public GET /server-list (group_name+server_name only,
no auth required) for ticket create page
- verified: 13 checks (frontend/backend/db/column/syntax)