[v0.91.8][csdlc-v2] Add Rust GitHub action command surface

[danielbaustin]

Closes #5655

Summary

• Add the Rust-only csdlc-github command with typed run and schema surfaces.
• Add typed GitHub action request/result schemas for issue create/update/comment/close/read and PR state observation.
• Enforce operation markers and exact post-mutation readback for issue create/comment/update/close, including exact updated body, labels, and assignees.
• Add operator guidance for the repo-native C-SDLC v2 GitHub action surface.
• Repair the CI strict Clippy blockers reported by csdlc-v2-standalone without changing behavior.

Validation

• Rebased onto origin/main 1facdf209.
• TMPDIR=/Volumes/FastWork/adl-builds/5655-tmp CARGO_TARGET_DIR=/Volumes/FastWork/adl-builds/5655-csdlc-v2-target cargo clippy --locked --manifest-path csdlc-v2/Cargo.toml --all-targets -- -D warnings passed.
• TMPDIR=/Volumes/FastWork/adl-builds/5655-tmp CARGO_TARGET_DIR=/Volumes/FastWork/adl-builds/5655-csdlc-v2-target cargo test --locked --manifest-path csdlc-v2/Cargo.toml --test gate_github_actions passed 2/2.
• TMPDIR=/Volumes/FastWork/adl-builds/5655-tmp CARGO_TARGET_DIR=/Volumes/FastWork/adl-builds/5655-csdlc-v2-target cargo test --locked --manifest-path csdlc-v2/Cargo.toml passed, including gate_github_actions 2/2 and Doc-tests csdlc_v2 1/1.
• csdlc-doctor --repo . --issue 5655 passed at reviewed generation 19.
• Boole exact-head read-only review was CLEAN for 1eb3e59819222fe59a590abbbc3b18bbe19643d1 after the CI strict Clippy repair.