feat(#613): the duel between two regulars, on the TV lobby

[mholzi]

Closes #613.

The code asked for this

get_player_standing justifies the lobby line in its own docstring: it is "supposed to start a rivalry". Only the solo view was ever built.

It reverses #371 on purpose

#371 sends each player only their own standing, and #624 kept that posture this afternoon — per-player, not broadcast, with the reasoning in the code.

A head-to-head on the TV puts two people's record in front of the whole room. That is a reversal, not an extension, and it is a taste call rather than a technical one: at home it is exactly the fun; at a party with colleagues "Ben 0–5" can be the moment someone stops playing. Markus made the call.

So the reversal is bounded:

• TV and admin only. The phones never receive it — a plain broadcast would have been one word shorter and would have undone House Championship — persistent all-time leaderboard on lobby + TV #371 everywhere.
• Lobby only. Mid-game it would compete with the question for the same screen.
• Silent until a pair has met twice. "1–0" after one shared game reads like a record and is a coincidence.

Details that are decisions

The winner of a meeting is between those two. Not the game's overall winner — Cara topping the table settles nothing between Anna and Ben.

A draw counts as a meeting and goes to nobody.

The most-met pair wins when several regulars are present, with ties broken alphabetically so the TV does not flicker between equals when someone rejoins.

"Last 90 days" is stated, not implied. The detailed history prunes at RETENTION_DAYS / MAX_DETAILED_RECORDS, so an all-time claim would be one the data cannot support. Extending it needs a pairwise rollup in the unpruned map, growing quadratically in players — not worth it for a lobby line.

Tests

tests/test_head_to_head_613.py: the single-meeting silence, the duel itself, the meeting winner vs the game winner, draws, the most-met pair among three, games only one of them played, a lobby of one, the lobby-and-TV-only wiring including the absent plain broadcast, the 90-day label in three languages, and name escaping.

Run against the unfixed code: 10 of 10 failed.

Suite 2103, ruff clean, mypy clean.