[OL-00] Freeze sidecar-only Change ID persistence

[jackieismpc]

Summary

Completes the large task OL-00: Change ID 写入路径 spike 与设计冻结 in docs/development/plan/plan-20260822.md.

• Adds and registers commit_change_id_header_spike, covering real Git header compatibility and sidecar-only object closure.
• Freezes Libra writes to sidecar-only; existing change-id headers are read-only import compatibility.
• Updates ADR-OL-04, the internal design document, the OL-00 conclusion, and CH-01/CH-03 handoff constraints.
• Includes the user-authorized no-behavior Rust CI prerequisite fixes for stable clippy and rustdoc.

Verification

• cargo +nightly fmt --all --check — PASS with nightly 1.100.0 (2026-08-24).
• RUSTUP_TOOLCHAIN=stable LIBRA_SKIP_WEB_BUILD=1 cargo clippy --all-targets --all-features -- -D warnings — PASS with stable 1.98.0.
• RUSTDOCFLAGS="-D rustdoc::broken_intra_doc_links" RUSTUP_TOOLCHAIN=stable LIBRA_SKIP_WEB_BUILD=1 cargo doc --no-deps --all-features — PASS with stable 1.98.0.
• RUSTUP_TOOLCHAIN=stable LIBRA_SKIP_WEB_BUILD=1 CARGO_PROFILE_TEST_DEBUG=0 CARGO_BUILD_JOBS=1 RUST_MIN_STACK=16777216 cargo test --test commit_change_id_header_spike — PASS, 2 passed.
• Web/UI-specific checks were not run because this change only covers the backend Rust spike and documentation.

Independent code review completed with PASS; the plan records OL-00 as remote-pending pending upstream CI/PR evidence.