[Phase 15] Document supported prompts and end-to-end workflows

[cosentinode]

Scope

Document parser-backed prompt examples and end-to-end status, commit, sync, branch, PR, conflict, and policy workflows, including deferred replanning and stop-on-failure.

Acceptance Criteria

• Every documented prompt is accepted by tests.
• Unsupported shell/raw Git is not advertised.
• PR base precedence and commit/push/open-pr sequences are accurate.
• Failure examples show later steps do not execute.

Verification

• cargo test --locked -p bitbygit-core
• cargo test --locked -p bitbygit-tui
• git diff --check

Notes

Child of #17; depends on completed Phases 12 and 13.