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.

app/api/packages/[id]/load/route.test.ts

@@ -92,7 +92,7 @@ describe('POST /api/packages/:id/load', () => {
     // Response convention (v0.8.0): the FULL snapshot, same shape as GET /api/state.
     const body = (await res.json()) as {
       account: { cash: number };
-      simState: { clockMs: number; timeScale: number; paused: boolean };
+      simState: { clockMs: number }; // ISS-117
       planes: Array<Record<string, unknown>>;
       packages: Array<{ id: string; status: string; planeId: string | null }>;
     };