Fix two runtime-only bugs found on first live run: missing sidebar icons for the 4 facing-sheet units, and waxseed needing QuantizeFacingsFromSequence

Adds tools/check_assets.py — check-yaml does NOT resolve sprite file paths, so a
missing PNG only crashes at map load. This catches it statically.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

mods/vinylgod/rules/economy.yaml

@@ -268,6 +268,7 @@ garage:
 
 waxseed:
 	BodyOrientation:
+	QuantizeFacingsFromSequence:
 	RenderSprites:
 	WithSpriteBody:
 	Interactable:

tools/check_assets.py

@@ -0,0 +1,28 @@
+#!/usr/bin/env python3
+"""Verify every Filename: referenced by the mod's sequence yaml actually exists.
+
+check-yaml does NOT do this — missing sprites only surface as a FileNotFoundException
+when a map loads. Run this after adding art. Exits non-zero on any miss.
+"""
+import os, re, sys, glob
+
+MOD = os.path.join(os.path.dirname(__file__), '..', 'mods', 'vinylgod')
+missing = []
+checked = 0
+for y in glob.glob(os.path.join(MOD, 'sequences', '*.yaml')):
+    for i, line in enumerate(open(y), 1):
+        m = re.search(r'Filename:\s*(\S+)', line)
+        if not m:
+            continue
+        checked += 1
+        p = os.path.join(MOD, m.group(1))
+        if not os.path.exists(p):
+            missing.append(f'{os.path.basename(y)}:{i}  {m.group(1)}')
+
+print(f'checked {checked} sprite references')
+if missing:
+    print(f'MISSING {len(missing)}:')
+    for m in missing:
+        print('  ' + m)
+    sys.exit(1)
+print('all sprite files present')