Fixed world clock: no player time controls (ISS-117)

The world always runs at WORLD_TIME_SCALE = 24 (lib/worldClock.ts). A server
background tick (instrumentation.ts -> startBackgroundTick, 1 s interval)
advances the sim with no open browser; idle-pause freezes the clock exactly
while no plane is flying or in repair. Fresh worlds start year 2000
(STARTING_CLOCK_MS in seed.ts).

- Removed: POST /api/sim + OpenAPI entry, applyTimeControls/clampTimeScale,
  lib/timeScale.ts, LeftPane pause button + scale slider machinery,
  ISS-057 slow-on-landing/resume in flyPlane.
- Snapshot simState is now { clockMs } only; client extrapolates at the fixed
  rate between polls and freezes while idle (useSimClock).
- New test-only hook POST /api/test/set-timescale behind FLIGHT_TEST_HOOKS=1
  (sibling of set-health); all e2e setScale helpers call it, afterEach restores
  the world rate. E2E pause tests replaced by idle-pause assertions; sim.spec.ts
  activates the world via set-health + /repair for advance/expiry tests.

lib/game/state.ts

@@ -73,7 +73,9 @@ export interface PackageState {
 
 export interface StateSnapshot {
   account: { cash: number; reputation: number };
-  simState: { clockMs: number; timeScale: number; paused: boolean };
+  // ISS-117 (v0.52.0): the world rate is a fixed constant (WORLD_TIME_SCALE), not per-save state —
+  // only the clock itself is reported here.
+  simState: { clockMs: number };
   planes: PlaneState[];
   packages: PackageState[];
   // Market reference data (v0.10.0) — static per build, sent with every snapshot so
@@ -135,7 +137,7 @@ export async function getStateSnapshot(): Promise<StateSnapshot> {
 
   return {
     account: { cash: accountRow.cash, reputation: accountRow.reputation },
-    simState: { clockMs: simRow.clockMs, timeScale: simRow.timeScale, paused: simRow.paused },
+    simState: { clockMs: simRow.clockMs },
     catalog: catalogEntries(),
     fuelPricePerL: FUEL_PRICE_PER_L,
     sellFraction: SELL_FRACTION,