Prepare Vex v0.0.1 release

[LunaStev]

Summary

• harden lockfile, managed Git checkout, installer temporary-file, and CLI argument boundaries for v0.0.1
• document installation, platform baselines, compiler compatibility, and the release procedure
• add integration coverage for CLI help and errors, relocatable path locks, compiler discovery, and dry-run schema rejection

Why

v0.0.1 is the first public Vex release. Its package-manager contract needs to be reproducible and portable before release, with clear compatibility and recovery guidance.

Behavior

• path dependency locations are locked relative to the project whenever possible
• locked Git commits must be complete hexadecimal object IDs
• managed Git operations restrict external transports and reject unsafe managed-dependency links
• command help remains read-only and invalid arguments fail without mutation
• compiler discovery and dry-run schema v1 validation remain explicit contracts
• no registry, publish command, workspace, or global cache is introduced

Validation

• python3 x.py check
• 22 Rust unit tests and 8 integration tests passed
• formatting, Clippy with warnings denied, and locked build passed
• native package, checksum, compiler, locked/offline, and raw-option rejection smokes passed