Fix backwards controls + the exe's bare-capsule avatar

Two real bugs from the last change, both only visible in a real run:

1. Controls reversed: the third-person SpringArm3D had a 180° Y rotation
   that put the camera IN FRONT of the player looking back -- a mirror, so
   W read as backward and mouse pitch as inverted. SpringArm3D extends its
   child along +Z, not -Z; with no rotation the camera sits behind the
   player (+Z world) and looks -Z straight at them. Verified the vectors
   headless: camera behind, W decreases Z, mouse-up looks up.

2. Bare capsule instead of an avatar in the .exe: avatar_catalog.gd reads
   assets/avatars/catalog.json with FileAccess.open(), but the export used
   `all_resources` + empty include_filter, which does NOT pack plain .json
   files. ensure_catalog() failed -> no loadout -> build_current_avatar()
   returned null -> capsule stayed visible. From source it worked because
   res:// is the real filesystem. Fixed: include_filter="*.json" in both
   export presets (verified catalog.json + the .glb pack are now in the
   exported .pck).

- scripts/verify_export_contents.gd + a checkpoint-runner step: export a
  pack and assert the non-resource runtime files are inside it. This is
  the guard for the "works from source, broken in the .exe" class.

Client-side -- rebuild the exe.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_015jtxAiu5dAW4WxCNdGkrkJ

scripts/run_checkpoint_tests.py

@@ -180,6 +180,17 @@ def main():
                     fc_env["GODOT_BIN"] = godot_bin
                     r = run(["bash", str(fc_script)], env=fc_env)
                     results["fresh-clone boot"] = r.returncode == 0
+
+                # Export packaging: the game reads some files (catalog.json)
+                # via raw FileAccess, which `all_resources` export doesn't
+                # pack unless include_filter covers them. Passes from source,
+                # bare capsule in the .exe. This guards that.
+                ec_script = ROOT / "scripts" / "verify_export_contents.gd"
+                if ec_script.exists():
+                    print("\n--- scripts/verify_export_contents.gd ---")
+                    r = run([godot_bin, "--headless", "--path", str(ROOT),
+                             "--script", "res://scripts/verify_export_contents.gd"], env=godot_env)
+                    results["export packaging"] = r.returncode == 0
         finally:
             server_proc.terminate()
             try: