test(env): cover UTF-8 .env values in load_env_file (#771)

Re-lands the #771 squash, which GitHub built against a stale base;
the merged commit was orphaned and never reached main.

tests/test_env_file_utf8.py

@@ -0,0 +1,17 @@
+from lib import env
+
+
+def test_load_env_file_reads_utf8_regardless_of_locale(tmp_path):
+    # setup_wizard writes .env with encoding="utf-8"; the loader must read it
+    # back with the same encoding instead of the platform default (cp1252 on
+    # most Windows locales), or non-ASCII values raise UnicodeDecodeError.
+    env_path = tmp_path / ".env"
+    env_path.write_text(
+        "# café notes ☕\nDISPLAY_NAME=Zoë\nAPI_LABEL=日本語キー\n",
+        encoding="utf-8",
+    )
+
+    loaded = env.load_env_file(env_path)
+
+    assert loaded["DISPLAY_NAME"] == "Zoë"
+    assert loaded["API_LABEL"] == "日本語キー"