feat(examples): Basic, a ball simulation with a bug to find

The example was a placeholder that printed which build it was. It is
now a headless simulation of five balls dropped onto a 10 cm floor
slab at 60 ticks a second, with a bug planted the way such bugs are
written: collision is checked only where each step lands, so the ball
dropped from 60 m, at 34 m/s, steps over the slab and falls forever.

It shows the consumer side end to end:
- Basic.DebugShim forwards Pump, Advance, QuitRequested, Log, Check,
  Emit and Sample to Crafter.Debug in debug builds and does nothing in
  plain ones, so the simulation and main have no #ifdef but the
  session's.
- Basic.DebugCommands, compiled only when Debug::Use returns true,
  registers World_Spawn, World_Reset, World_Clear and Ball_Get, and
  watches for the physics, the floor and the balls.
- The simulation checks each ball stays above the floor, emits Bounce
  and samples the fastest ball, so `pause --on-check`, `wait --event`
  and `trace --history` have something to show.

Driven over the real transport, it shows the whole loop: `log --level
warn` names the ball, `pause --on-check` stops the frame it fails,
`set physics.substeps 4` and `call World_Reset` show the fix holds
before any code changes. The plain build simulates ten seconds and
prints that one ball fell through. Its agent notes describe the app
without the bug.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

examples/Basic/interfaces/Basic.DebugCommands.cppm

@@ -0,0 +1,14 @@
+// SPDX-License-Identifier: MIT
+// SPDX-FileCopyrightText: Copyright (C) 2026 Catcrafts®
+
+// What an agent can call and read in a debug build. project.cpp compiles
+// this module only when Debug::Use added Crafter.Debug, so the plain build
+// has none of it.
+export module Basic.DebugCommands;
+import Basic.World;
+
+export namespace Basic {
+    // Registers the commands and watches on `world`, which must outlive the
+    // Session.
+    void RegisterDebug(World& world);
+}