fix: theme color parsing breaks on #rgb shorthand hex (#1213)

* refactor: add pure hexToRgb helper that handles #rgb shorthand

* fix: handle #rgb shorthand hex in theme color parsing

* test: hexToRgb expands shorthand and rejects invalid input

tests/test_hex_to_rgb_js.py

@@ -0,0 +1,49 @@
+"""Pin the pure hexToRgb helper (static/js/color/hex.js).
+
+Driven through `node --input-type=module` (same approach as test_compare_js.py);
+skips when `node` is not installed.
+
+Regression: theme.js parsed hex with fixed substring(0,2)/(2,4)/(4,6) slices, so
+a 3-digit shorthand like "#abc" produced NaN channels (the color picker already
+expanded shorthand correctly — theme parsing did not).
+"""
+import json
+import shutil
+import subprocess
+from pathlib import Path
+
+import pytest
+
+_REPO = Path(__file__).resolve().parent.parent
+_HELPER = _REPO / "static" / "js" / "color" / "hex.js"
+_HAS_NODE = shutil.which("node") is not None
+
+
+def _rgb(hex_str: str):
+    js = (
+        f"import {{ hexToRgb }} from '{_HELPER.as_posix()}';"
+        f"console.log(JSON.stringify(hexToRgb({json.dumps(hex_str)})));"
+    )
+    proc = subprocess.run(
+        ["node", "--input-type=module"],
+        input=js, capture_output=True, text=True, cwd=str(_REPO), timeout=30,
+    )
+    assert proc.returncode == 0, proc.stderr
+    return json.loads(proc.stdout.strip())
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_shorthand_expands():
+    assert _rgb("#abc") == {"r": 0xAA, "g": 0xBB, "b": 0xCC}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_full_form_and_no_hash():
+    assert _rgb("#ff8800") == {"r": 255, "g": 136, "b": 0}
+    assert _rgb("ff8800") == {"r": 255, "g": 136, "b": 0}
+
+
+@pytest.mark.skipif(not _HAS_NODE, reason="node binary not on PATH")
+def test_invalid_returns_null():
+    assert _rgb("nothex") is None
+    assert _rgb("") is None