fix(index): refresh missing default mcpplibs index

[Sunrisepeak]

Summary

• require the default mcpplibs index clone itself when checking index freshness
• add regression coverage for mixed-cache homes that contain other xlings indices but no mcpplibs
• bump release metadata to 0.0.36 and keep the binary --version source in sync
• add an e2e guard that compares mcpp --version with mcpp.toml

Verification

• mcpp build
• MCPP=<0.0.36 binary> bash tests/e2e/01_help_and_version.sh
• mcpp test
• temporary mixed-cache repro: MCPP_HOME=<tmp-with-xim-pkgindex-only> <0.0.36 mcpp> search libarchive found compat:compat.libarchive
• current xlings project: MCPP_HOME=/home/speak/.mcpp <0.0.36 mcpp> build