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/deriveEvents.test.ts

@@ -47,7 +47,7 @@ const basePackage = (id: string): PackageState => ({
 
 const snapshot = (over: Partial<StateSnapshot> = {}): StateSnapshot => ({
   account: { cash: 20_000, reputation: 10 },
-  simState: { clockMs: 0, timeScale: 1, paused: false },
+  simState: { clockMs: 0 },
   planes: [basePlane('plane-starter')],
   packages: [],
   catalog: CATALOG,
@@ -59,7 +59,7 @@ const snapshot = (over: Partial<StateSnapshot> = {}): StateSnapshot => ({
 describe('diffSnapshots', () => {
   it('returns [] for identical snapshots (only clock/cash drift)', () => {
     const prev = snapshot();
-    const next = snapshot({ account: { cash: 21_000, reputation: 11 }, simState: { clockMs: 60_000, timeScale: 1, paused: false } });
+    const next = snapshot({ account: { cash: 21_000, reputation: 11 }, simState: { clockMs: 60_000 } });
     expect(diffSnapshots(prev, next)).toEqual([]);
   });