Priority Translate button: enqueue near the front of the lane queue

[znsoftm]

Card Translate (「翻译」) now priority-enqueues a paper at the head of its fast/slow lane, so a click runs soon instead of waiting behind the whole backlog.

Stacked on cursor/papers-load-perf-1d37 (the current papers UI + dual-lane translate queue). main does not yet contain the translation system.

Semantics

POST /papers/translate accepts "priority": true on a single id:

• Insert / bump at lane head. The paper is placed at index 0 of its lane (fast ≤50 pages, slow 51–100). It is the next job that lane will tryPop after currently running work.
• Does not preempt running jobs. A paper that is already running is still rejected (正在翻译中). Priority only reorders the pending lane queue.
• Already queued: bump to the lane head (single entry, no duplicate). A second click without priority remains a no-op skip.
• Translate-all / auto-translate: ignore priority and keep FIFO tail append, so the backlog is not reversed.
• Page-limit skip: papers with page_count > 100 still reject with too_many_pages; no button is shown.
• Auth: same manage/auth as other translate enqueue (authorizeSettings / can_manage). Anonymous visitors never see the control.

UI

Shared renderPaperCard (catalog + Hugging Face Daily):

State	Control
Untranslated, has local PDF	Translate / 「翻译」 (priority: true)
Already queued	Prioritize / 「优先」 (bump to lane head)
Done	Re-translate / 「再次翻译」 (force + priority)
Running or >100 pages	No button

Test plan

• TestPriorityEnqueueInsertsAheadOfNormalQueue — new priority id sits in front of tail-queued items
• TestPriorityEnqueueBumpsAlreadyQueued — already-queued id moves to head; no duplicate; non-priority second click is a no-op
• TestPriorityEnqueueDoesNotPreemptRunning — running id rejected; next tryPop is the prioritized paper
• TestPriorityEnqueueStaysInLane — slow-lane priority does not jump the fast queue
• TestPriorityEnqueueIgnoredForTranslateAll — {all:true, priority:true} stays FIFO
• TestPapersTranslatePostPriorityNearFront — HTTP priority:true requires auth and lands at the lane head
• Papers HTML i18n + priority: true payload assertions
• go test ./internal/api/ (full package, pass)
• Manual /papers: Translate → Translate pending → Prioritize on Gamma; queue became 2401.00003, 2401.00001, 2401.00002 (Gamma at the lane head). Status: 「已移到队列最近位置。」