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>

tests/core/graph.test.ts

@@ -452,7 +452,7 @@ describe('variable commands', () => {
 
     stack.execute(new RenameVariableCommand(behavior.id, 'speed', 'velocity'));
     expect(behavior.variables[0]!.key).toBe('velocity');
-    expect(behavior.props).toEqual({ enabled: true, runInEditor: false, velocity: 0 });
+    expect(behavior.props).toEqual({ enabled: true, runInEditor: false, runWhilePaused: false, velocity: 0 });
     expect(object(logic).overrides).toEqual({ velocity: 5 });
     expect(findNode(behavior.graph, nodes.speed.id)!.ports).toEqual([{ key: 'velocity', kind: 'number' }]);
     stack.undo();
@@ -477,7 +477,7 @@ describe('behavior serialization', () => {
     const loaded = findAsset(roundTrip(project), behavior.id) as BehaviorAsset;
     expect(loaded.variables).toEqual(behavior.variables);
     expect(loaded.graph).toEqual(behavior.graph);
-    expect(loaded.props).toEqual({ enabled: true, runInEditor: false, speed: 0 });
+    expect(loaded.props).toEqual({ enabled: true, runInEditor: false, runWhilePaused: false, speed: 0 });
 
     const raw = serializeProject(project) as {
       assets: { id: string; graph?: { nodes: unknown[]; edges: unknown[] } }[];