feat(ci): verify Cargo.lock reproducibility across Linux, macOS, and Windows

[gospeltout]

Description

This PR implements cross-platform Cargo.lock reproducibility verification for StarForge. It ensures that locked builds (--locked) do not mutate dependency resolution, fail unexpectedly, or introduce platform-dependent lockfile drift across Linux, macOS, and Windows.

Closes #654

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Changes Made

• Core Verification Engine (src/utils/cargo_lock.rs): Implemented verify_cargo_lock_reproducibility to validate lockfile immutability, check manifest/lockfile existence, check toolchain availability, detect out-of-sync dependency errors, generate line-by-line diff summaries, and auto-restore mutated lockfiles.
• CLI Subcommand (starforge verify lockfile): Added starforge verify lockfile to src/commands/verify.rs with --path, --json, and --strict options.
• CI Workflows: Enforced post-build git diff --exit-code Cargo.lock checks across Linux, macOS, and Windows matrix targets in .github/workflows/ci.yml, .gitlab-ci.yml, and Jenkinsfile.
• Documentation: Updated DEVELOPER_GUIDE.md, CI_ENFORCEMENT.md, and BUILD_TROUBLESHOOTING.md with cross-platform lockfile rules, CLI usage, and resolution troubleshooting instructions.

Testing

How has this been tested?

Describe the tests you ran and how to reproduce them.

• Unit tests added/updated
• Integration tests added/updated
• Manual testing performed

Command output verification:

cargo test --lib utils::cargo_lock
cargo test --test cli_cross_platform
cargo run -- verify lockfile --json
cargo fmt --all --check

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