tests: annotate documented dwells in group-Y presence specs (determinism lint)

lint:determinism failed the staging deploy (run 33200086355) on 5 lines in
the presence specs committed 8/28: overlay-repaint dwells before settledShot,
the best-effort #canvas focus, and the sampling cadences of the two explicit
presence-eviction poll loops. All are intentional; annotate them the way
3d-viewer-*.spec.ts does so the guard accepts them.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LvvARNMxQrq17vogn3REMU

tests/web/presence-ghost-peer.spec.ts

@@ -106,7 +106,7 @@ for (const mode of ['half-open', 'unclean-close'] as const) {
       const present = await bob.locator('[data-presence-user="alice"]').count();
       seen.push(`+${Math.round((Date.now() - t0) / 1000)}s:${present}`);
       if (present === 0) { ms = Date.now() - t0; break; }
-      await bob.waitForTimeout(5000);
+      await bob.waitForTimeout(5000); // eslint-disable-line -- documented sampling dwell: presence-eviction probe cadence inside an explicit bounded loop
     }
     const sockets = await alice.evaluate(() => (window as unknown as { __wsReport(): unknown }).__wsReport());
     // eslint-disable-next-line no-console