Mantle 0.1.2

Fix Rust and native dependency compilation inside confined Mantle sessions, with updated setup and qualification documentation.

• Select GCC for the Rust linker and C compiler, and G++ for the C++ compiler, for new agent and supplementary execution requests.
• Preserve the existing filesystem and network confinement boundaries.
• Document the successful live KubeVirt build check, workspace isolation and gateway checks, explicit Cargo proxy configuration for standalone exec, and remote exit-status handling.
• Pin the documentation quickstart to this source release.

This is an early source release, with source archives and no prebuilt release binaries. Build the laptop CLI and static worker binaries from the same tag; upgrade workers when no sessions are active.

Real ChatGPT device login, authenticated model/tool turns, token refresh and complete live lifecycle parity remain unverified. Codex uses the same Substrate terminal transport as Claude, which may retain terminal output. See docs/evidence/codex-compatibility.md and the linked acceptance audit for the observed limits.

Validation: 187 top-level Rust tests, all 336 native ESS scenarios, repository lint/specification/documentation checks, and all three x86_64-unknown-linux-musl worker release builds passed locally. Required exact-commit GitHub checks are verified before publication.