split(configs[i], "=") splits on ALL '=' characters, truncating
SS 2022-blake3 passwords that contain base64 padding (==) +
colon-delimited IMK. Replaced with split_first() which splits
only on the first '=', keeping the full password intact.
- Added split_first() utility to string.h/string.cpp
- Replaced all 15 key=value split() calls in subparser.cpp
- Verified with Docker build + Surge/Clash output test
