Record the Honkai Impact 3rd source and what its dates are worth

SOURCES.md § 13 declined this game's only known source partly because every
boundary was a week bucket, and we have now built a different source with that
same objection standing. Leaving that contradiction unwritten is how a later
pass rediscovers the trade the expensive way, so § 14 records the decision
itself: the conduct evidence, which three of § 13's four objections arustats
answers, which one it does not, and that any source stating a date per event
retires it. § 13 is marked superseded rather than rewritten — its verdict on
marisaimpact.com still stands and was not re-tested.

AGENTS.md gets the same warning where a parser author will hit it, because the
estimate is not visible from the code: the numbers look like every other
day-precision date in the project.

Also corrects the counts this game made false — nine parsers, twenty sources,
nineteen games. The "stopped working at eighteen" passages are left alone: they
date the settings-panel redesign, and bumping them would falsify the history
rather than update a count.

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

docs/PRD.md

@@ -59,7 +59,7 @@ have a source — this table is the launch scope, not a roster to keep in sync.
 
 Adding a game must require no change to `GachaEvent` — only a `GameId` entry, its `games.ts`
 metadata, and a source registration. That is the test of whether the data model is right, and it has
-held: the eighteen games here have cost the event schema nothing. Per-game *metadata* does occasionally
+held: the nineteen games here have cost the event schema nothing. Per-game *metadata* does occasionally
 grow (Reverse: 1999 needed `resetHourLocal` for a 05:00 reset), which is a different file and moves
 no stored key. A game may have several sources; see `docs/INGESTION.md` § Three layers.
 
@@ -90,7 +90,7 @@ default `"game"` — the board every existing reader already has). Merged, the o
 `endingSoonestFirst`, the same comparator behind the list's "Ending soonest" (F2), so the two views
 cannot mean different things by the same words and an unannounced end still sorts behind every dated
 one rather than claiming a place in the queue. Merged there is also no lane heading to say whose
-event a bar is, and hue alone cannot answer that once eighteen games share a stack — so each bar
+event a bar is, and hue alone cannot answer that once nineteen games share a stack — so each bar
 carries its game's short name, with the full name in its tooltip. A bar too narrow for a tag and a
 title both keeps the title: a chopped game name reads as a broken word, and the hue and the tooltip
 still answer it.