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.

components/right-pane.test.ts

@@ -54,7 +54,7 @@ function pkg(over: Partial<PackageState> & Pick<PackageState, 'id'>): PackageSta
 function snap(planes: PlaneState[], packages: PackageState[] = []): StateSnapshot {
   return {
     account: { cash: 0, reputation: 0 },
-    simState: { clockMs: 0, timeScale: 1, paused: false },
+    simState: { clockMs: 0 },
     planes,
     packages,
     catalog: CATALOG,