The clock: turn windows, the deadline, and the impound, all derived from timestamps #11

Intent. Make the game asynchronous but not stalled — a turn that goes unplayed for its window becomes a pass, and a table that reaches its deadline without an accord is impounded — with no timers, no background job, nothing but arithmetic on rows at read time.

Done looks like

• [ ] A small src/clock.ts: given a game, its acts and a now, it says whose turn it is, when that turn lapses, how many turns have lapsed unplayed, and whether the deadline has passed. Pure, now injected, fully tested.
• [ ] Reading or acting on a table first settles the clock: lapsed turns are written as real pass acts by the engine (seat marked, reason lapsed), and a passed deadline settles the table as impounded with every seat scored zero and everything revealed exactly as a binding accord reveals it.
• [ ] turn_seconds (default 6h) and deadline_seconds (default 24h) are set when the table opens, validated to a sane range, and shown on the page and in the API.
• [ ] tableState carries turn_ends_at and deadline_at as ISO strings; the page renders a countdown without layout shift, and without JavaScript still shows the absolute time.
• [ ] Tests advance a fake clock: three windows pass and three passes appear once; the same read twice does not write twice; the deadline impounds exactly once and emit("table.impounded", …) fires once.

Files src/clock.ts (new), src/clock.test.ts (new), src/actions.ts, src/db.ts, src/page.ts, src/actions.test.ts.

Risks Lazy catch-up is idempotent or it is a bug — two readers arriving at once must not each write the pass. Do the catch-up inside one transaction with a guard on the act count.

Brief that fits @hearth — honest about what really runs, with a recoverable state. (A person assigns.)

Split. RULES.md §8 is two clocks. The turn window — a window that passes unplayed becomes one pass act marked lapsed, several at once if several passed — needs only the ledger (#8, merged) and src/when.ts (#20, merged), and it is what keeps a real table moving when somebody goes quiet; it is now #77, ready.

This issue keeps the deadline and the impound, which are an ending and belong with #10 — the dependency is right and stays. #53 (a silent table still passes) sits on top of both.

Note for whoever takes the deadline and the impound: #83 changes the deadline's floor from 2 × turn window to the arithmetic of a binding (quorum + 1 windows, plus slack), because on today's defaults a 5- or 6-seat table cannot bind before its deadline if the seats use their windows. Read the deadline rule from the constants after that lands, not from the numbers written here.