Audiobookshelf import in setup: follow-ups from #395 #396

Follow-ups from #395 (Audiobookshelf import inside setup, #366 part 1). None loses data: Apply re-matches against the index at apply time.

Correctness (low)

• The scan gate only covers Connect in the setup step. The map step's Start, Apply, and all of Settings > Import stay ungated, so a review planned mid-scan lists not-yet-scanned books as unmatched. Gating inside ImportFlow or on the server would also block imports during routine rescans, so this needs a decision.
• At the abs step with no books library yet, Connect is enabled and the review matches nothing. Nothing says the folder step comes first (needs a string in six locales).
• Pre-existing, seen during verification: discarding an import while its "books not matched" list is open logs a 404 for GET /api/v1/admin/imports/{id}, because the deleted import's detail query is refetched (use-discard-import.ts, invalidateImported).

Polish

• An http address that redirects to self-signed https gets the abs_certificate hint "use the plain http:// address", which is what the admin typed.
• The setup step's new-tab Match offer has no ExternalLink icon or "opens in a new tab" text, which the removed link had.
• The history card's offer shows a mid-scan count while a scan runs (same as Overview and Books today).
• At 390 px the account-map table (min-width 440px) scrolls inside its box, and the "Import into" dropdowns are cut off. The setup step's extra padding makes it narrower than Settings > Import.
• While mapping in setup, the step shows two Back buttons: the map card's and the step's.
• setup-model.ts imports scanActive from @/api/hooks, the only model that loads the hooks module. hasBookLibrary in offerMatch overlaps UnmatchedPrompt's own hide at count 0. The scan-gate test waits on the real 1 s poll.
• Native de/es/fr/it/pt read of errors.absCertificate, imports.failure.abs_certificate, setup.abs.import and setup.abs.waitScan.