fix: count down to a game's reset, not to UTC midnight

A source that prints "August 19, 2026" and no time is stored at 00:00Z,
which is a placeholder for "somewhere in this day" rather than a claim
about when the day opens. The countdown read it literally, which turns it
into exactly that claim — and the UTC day is nobody's. Wuthering Waves
events dated the 19th were still running three hours after we had retired
them, because a European player's day opens at 04:00 on a UTC+1 server;
Asia was four hours out the other way and America nine. Sixty-two of the
eighty-six published events were affected, across ten of thirteen games,
so the reader was reading a wrong number far more often than a right one.

A day-precision boundary now resolves to the reset that opens that
game-day on the reader's server — the same grid daily.ts keys every tick
by, and the only clock we hold for a game. That is a reading of the date
the source printed, not a time invented for it: nothing stored moves, no
event ID moves, and the parsers still refuse to guess.

Two boundaries are never re-anchored. A regionEnds value is already the
instant a source stated per server, so anchoring it would throw a fact
away. And an event the reader typed in was resolved by readerInstant in
their own timezone, which is a stated time too — theirs.

Co-Authored-By: Claude Opus 5 (1M context) <[email protected]>

docs/PRD.md

@@ -287,6 +287,12 @@ The app's entire value is that the dates are right. Therefore:
 - An event whose confidence is below threshold, or whose sources disagree, is not published at all
   until a human approves it.
 - Every event links to its source so a skeptical user can verify in one click.
+- **A date with no time is resolved on the game's clock, never on UTC's.** Most sources print
+  "August 19, 2026" and no time of day, which is stored as 00:00Z — a placeholder, not an instant.
+  The countdown reads it as that game-day's server reset for the reader's region, because a literal
+  reading retires an event up to nine hours before the game does and the reader is standing in the
+  game while we say it. This is a reading of the date the source printed, not a time invented for
+  it, and the detail sheet says as much.
 
 An empty calendar is a recoverable disappointment. A confidently wrong end date is the failure this
 product exists to prevent.