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.

e2e/api.spec.ts

@@ -13,7 +13,7 @@ test('GET /api/version returns the app version from package.json', async ({ page
   expect(body.version).toBe(pkg.version);
 });
 
-test('GET /api/openapi serves the spec with all thirteen endpoints and the package.json version', async ({ page }) => {
+test('GET /api/openapi serves the spec with all twelve endpoints and the package.json version', async ({ page }) => {
   const res = await page.request.get('/api/openapi');
   expect(res.status()).toBe(200);
   expect(res.headers()['content-type']).toContain('application/json');
@@ -32,7 +32,6 @@ test('GET /api/openapi serves the spec with all thirteen endpoints and the packa
     '/api/planes/{planeId}/queue',
     '/api/planes/{planeId}/queue/cancel',
     '/api/planes/{planeId}/repair', // v0.39.0 (ISS-069)
-    '/api/sim',
     '/api/state',
     '/api/version',
   ]);