Clear MASTER_PASSWORD_HASH env var in test setup

Prevents leftover env vars from previous runs causing auth issues.
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

tests/robot/start_server.sh

@@ -11,6 +11,8 @@ mkdir -p "/tmp/aniworld_test_anime/Unknown Anime (2020)"
 mkdir -p "/tmp/aniworld_test_anime/Test Series (2024)"
 # Remove existing config so the app starts in an unconfigured state
 rm -f data/config.json
+# Clear any leftover MASTER_PASSWORD_HASH env var from previous runs
+unset MASTER_PASSWORD_HASH
 export DATABASE_URL="sqlite:////tmp/aniworld_test.db"
 export ANIME_DIRECTORY="/tmp/aniworld_test_anime"
 export ANIWORLD_TESTING="1"