feat: one California is the product, not a flag

Behind `?one=1` the merged board was something a visitor could not find
and did not get: the site still landed on the Bay Area, the left column
still offered two other boards, and clicking one still tore the board
down and built another. The board existed and the product did not change.

A bare URL is now one California. `?city=sf` and `?city=socal` still get
the dedicated boards, unchanged and on purpose — twenty-nine capture
guards and the `bay-area` and `socal` budget cells aim at those boards by
name and assert the `data-board` they land on, and a metro id falling
back to the merged board would not degrade them, it would make them
silently measure something else. `?one=0` forces the old arrangement, and
both `california` budget cells now pass it: their caps are the plain
state board's 440,000, and without it they would measure the merged board
that `california-one` already covers.

Also `CALIFORNIA.md`: what a single cohesive California is still missing,
measured rather than listed. Every district on the board by the latitude
of its centre is 1 / 23 / 26 / 1 / 2 / 54 across 32-37 N and **zero above
38 N** — 107 districts, 103 of them in two clusters four hundred
kilometres apart, and four hundred and fifty kilometres of northern
California with not one building on it. Eight airports, all Bay or LA.
Two ports, both in San Pedro Bay. Two freeways of twelve vertices each
across a thousand kilometres of state.

The scale is not the problem and the file says so first: the board is
32.50-42.05 N and -124.50 to -114.00 W at 1,919 m to the unit, every
feature on its real coordinate, nothing schematic. It is not too small.
It is empty.

src/main.ts

@@ -227,7 +227,7 @@ import type {
 import type { PresenceIndicator } from "./realtime/presenceIndicator.ts";
 
 /**
- * One full California, as **one pack**, behind `?one=1`.
+ * One full California, as **one pack** — and now the default.
  *
  * The first attempt at this nested each metro's built scene inside the state
  * board's under a similarity transform. The transform was right and the result
@@ -236,8 +236,41 @@ import type { PresenceIndicator } from "./realtime/presenceIndicator.ts";
  * one `City` carrying the state's landform and both metros' detail, so the
  * engine builds one world, one lattice and one terrain mesh. See that file for
  * the measured lattice cost and for the two merges that are not a union.
+ *
+ * ## Why it is no longer behind a flag
+ *
+ * Because a flag is a second product, and the whole point was to stop having
+ * three. Shipped behind `?one=1` the merged board was something a visitor could
+ * not find and did not get: `tera.lumbridgecorp.com` still landed on the Bay
+ * Area, the left column still offered two other boards, and clicking one still
+ * tore the board down and built another. The board existed and the product did
+ * not change.
+ *
+ * ## The three ways this resolves, and why the escape hatches are shaped so
+ *
+ * Default — no `?city=`, or `?city=california` — is **one California**.
+ *
+ * `?city=sf` and `?city=socal` still get the dedicated boards, unchanged. That
+ * is deliberate and it is not hedging: twenty-nine capture guards in
+ * `scripts/brand-assets` and the `bay-area` and `socal` cells of
+ * `scripts/performance-budget.mjs` aim at those boards by name and assert the
+ * `data-board` they land on. Making a metro id fall back to the merged board
+ * would not degrade those, it would make them silently measure and photograph
+ * something else — which is the exact failure the budget harness's own comment
+ * says the `data-board` assertion exists to catch. A named board stays a named
+ * board.
+ *
+ * `?one=0` forces the three-board product whatever the city is. One consumer
+ * needs it — the `california` budget cell, which is written against the *plain*
+ * state board's 440,000 cap and would otherwise measure the merged board that
+ * `california-one` already covers — and it is the honest way to say "the old
+ * arrangement" without spelling a board id.
  */
-const ONE_CALIFORNIA = new URLSearchParams(location.search).get("one") === "1";
+const ONE_PARAM = new URLSearchParams(location.search).get("one");
+const CITY_PARAM = new URLSearchParams(location.search).get("city");
+const ONE_CALIFORNIA =
+  ONE_PARAM === "1" ||
+  (ONE_PARAM !== "0" && CITY_PARAM !== "sf" && CITY_PARAM !== "socal");
 
 /**
  * The boards on offer — three, or **one**.