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/verify_export_contents.gd

@@ -0,0 +1,66 @@
+extends SceneTree
+## Exports a resource pack and checks that the files the game reads at runtime
+## via raw FileAccess (not as Godot resources) are actually inside it.
+##
+## `export_filter="all_resources"` packs scenes/scripts/imported assets but
+## NOT arbitrary files like assets/avatars/catalog.json -- which the avatar
+## system opens with FileAccess.open(). Missing it means the game runs fine
+## from source but the exported .exe shows a bare capsule instead of an
+## avatar. This is the guard for that class of bug.
+##
+## Run: godot --headless --path . --script res://scripts/verify_export_contents.gd
+
+const PACK_PATH := "res://.export_check.pck"
+
+## Files that MUST be in the pack for the game to work, that aren't Godot
+## resources (so they only get packed via export_presets include_filter).
+const REQUIRED := [
+	"res://assets/avatars/catalog.json",
+]
+
+## A resource we know should be there, as a sanity check that the pack loaded.
+const SANITY := "res://scenes/game.tscn"
+
+
+func _initialize() -> void:
+	var abs_pack := ProjectSettings.globalize_path(PACK_PATH)
+
+	var export := OS.execute(_godot_bin(), [
+		"--headless", "--path", ProjectSettings.globalize_path("res://"),
+		"--export-pack", "Linux", abs_pack,
+	], [], true)
+	if not FileAccess.file_exists(PACK_PATH):
+		_fail("export-pack produced no file:\n%s" % export)
+
+	if not ProjectSettings.load_resource_pack(PACK_PATH, false):
+		_fail("could not load the exported pack back")
+
+	if not FileAccess.file_exists(SANITY):
+		_fail("pack sanity check failed -- %s not found (pack may not have loaded)" % SANITY)
+
+	var missing := []
+	for f in REQUIRED:
+		if not FileAccess.file_exists(f):
+			missing.append(f)
+
+	DirAccess.remove_absolute(abs_pack)
+
+	if missing.is_empty():
+		print("=== SMOKE RESULT: PASS === (required non-resource files are in the export)")
+		quit(0)
+	else:
+		print("=== SMOKE RESULT: FAIL ===")
+		for f in missing:
+			printerr("  MISSING from export: ", f,
+				"  -- add its glob to export_presets.cfg include_filter")
+		quit(1)
+
+
+func _godot_bin() -> String:
+	return OS.get_executable_path()
+
+
+func _fail(msg: String) -> void:
+	printerr(msg)
+	print("=== SMOKE RESULT: FAIL ===")
+	quit(1)