A game can pause itself and set its own time scale (#167)

Until now only the editor toolbar could pause a running game. A pause
menu inside the game had no way to stop the world while its own graph
kept running, and there was no slow motion.

- Five new nodes: Pause game, Resume game, Is game paused, Set time
  scale and Time scale. Pause and resume take effect on the next frame.
- A game pause stops world time, physics, animations, particles and
  shader time. Only behaviors with the new "Run while paused" switch
  keep running.
- Set time scale 0 freezes the world but graphs keep running, as
  agreed in the issue.
- Play and Stop reset the time scale to 1, Load scene keeps it. The
  pause belongs to the scene, so Load scene and Restart unpause.
- The toolbar pause stays separate and also freezes the menu. When the
  game pauses itself the status line reads "The game paused itself".
- While paused, collision events are not reported, sounds keep
  playing, and the editor run ignores both nodes with a log line.

Findings:
- The first status line was longer than any before and got cut with
  an ellipsis. It is shorter now.
- The e2e harness did not know the key "p". It does now.

Tests:
- ./check.sh: 133 files, 1968 tests, exit 0 (before 132 / 1952)
- npm run build: exit 0
- GM_STEPS=18 fresh: ALL PASSED, 33 checks (before 26)
- 16 new unit tests: 8 catalog cases, game-pause.test.ts, editor run
- 7 new e2e checks in block 18i, driven by real keys in the game
- Six counter-checks all bite: behavior filter, collision lock, world
  time, editor run, clock reset and the game clock in the browser
- Check total 1217 in README is computed (1210 + 7), CI measures it

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

src/core/graph/nodes/index.ts

@@ -2,6 +2,7 @@ import { type NodeDef, registerNode } from '../NodeRegistry';
 import { Destroy } from './action/Destroy';
 import { PauseAnimation, PlayAnimation, StopAnimation } from './action/animationNodes';
 import { Emit } from './action/Emit';
+import { IsGamePaused, PauseGame, ResumeGame, SetTimeScale, TimeScale } from './action/gameTimeNodes';
 import { LoadScene } from './action/LoadScene';
 import { Log } from './action/Log';
 import { IgnoreOneWay } from './action/IgnoreOneWay';
@@ -236,6 +237,11 @@ export const BUILT_IN_NODES: readonly NodeDef[] = [
   Log,
   StopGame,
   RestartGame,
+  PauseGame,
+  ResumeGame,
+  IsGamePaused,
+  SetTimeScale,
+  TimeScale,
 ];
 
 for (const def of BUILT_IN_NODES) registerNode(def);