The same bug the camera had, still live in the default light rig

Three loose ends turned into four, because one of them was not a stale comment.

`cityDaylight()` closed its fog at 210/460 — numbers tuned when San Francisco's
230-unit board was the only one. Every caller who supplies an `Atmosphere`
overrides them, which is why this survived: the demo does, so nothing looked
wrong. A self-hoster who renders a city with no clock and no weather gets the
default path, and on the Bay Area's 1003 units that fog closes well inside the
city. It now scales to the board exactly as the camera limits do, with the old
constants preserved as the default for a caller holding a palette but no world.

The three that really were comments: socal.ts justified its `latScale` by
citing the 340-unit orbit cap and the 460-unit fog as things the engine
insisted on, and the engine stopped insisting when both became board-relative —
285 is now a choice the pack makes because its lot sizes and hill radii were
authored against it. CONTRACT.md and ARCHITECTURE.md still measured the
retention argument against a 336,864-point San Francisco that has been the
whole Bay Area for some time. And server/package.json listed five routes where
there are six.

None of these changed behaviour except the first. All of them would have gone
on quietly disagreeing with the pages that now cite them.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CONTRACT.md

@@ -37,8 +37,9 @@ asserting `GET /api/v1/health` → 200.
 ## 1. Stage and scene lifecycle
 
 Two designs both created `src/engine/stage.ts` with opposite lifecycles. The
-retention argument wins on measured cost: SF's heightfield is 484 × 696 =
-336,864 lattice points and `world.ts` records a ~1.0 s build. Disposing the city
+retention argument wins on measured cost: the Bay Area's heightfield is 0.53M
+lattice points and about 2.3 s to build — it was 336,864 and ~1.0 s when the
+pack was San Francisco alone, and it grew, which is the point. Disposing the city
 every time someone steps into an office and paying a second of rebuild on the
 way out is not acceptable.