merge duplicate listings across indexes, unify key hints and toasts

[melqtx]

Two bodies of work that were in flight together on this branch.

Cross-index merge (new)

The same torrent listed on three indexes was three rows, each magnet carrying a different partial tracker set. Now it is one row, and the magnet queued announces to the union of every tracker those listings knew about — finding peers no single listing would have led to.

• internal/provider/merge.go — Result.InfoHash() (hex, base32, uppercase), Merge, MergeAll, Result.Trackers(). Trackers union; seeders/leechers take the higher scrape; Trusted ORs; size fills from whichever index knew it; AlsoOn records the others.
• Non-tracker magnet params (webseeds, peer hints) deliberately stay with the keeper — inheriting one index's idea of where to fetch bytes is a bigger trust step than widening who we ask about peers.
• MergeAll picks its keeper by a total order independent of arrival, so a concurrent fan-out is reproducible. The tracker union is sorted for the same reason.
• Results with only a detail page keep their own row: no magnet, no infohash to compare, and resolving every page would cost a round trip each.
• The better-scoring listing keeps the title, since that is what the tag parser, group label, and ranker read.
• Autopilot merges before ranking, so a release on four indexes competes for one slot instead of four.

UI: rows show yts+2, the status line counts folded listings, and the graph detail panel reports the tracker total.

UI/UX pass

Single keymap table feeding both the footer strip and the ? card so they cannot drift, unified toast system, and preview/downloads refinements.

Notes

• Queuing no longer jumps to downloads; ^d jumps there from anywhere instead, including mid-typing (it is a chord so it needs none of the guards a letter does). Costs emacs delete-forward in text fields; the delete key still works.
• Full suite, go vet, and -race green. New tests cover the merge primitive, streaming ingest, determinism under shuffled input, and the keybind across every screen.