Spec closure: active spec/doc convergence and workflow safety

[ganesh47]

Close the honesty gap between the active spec/docs and the shipped product.

Scope:

• remove roadmap / first-slice language from the active spec
• make the active spec fully match the shipped command surface
• tighten dirty-worktree / GitHub mutation safety where the spec already claims it
• align README and current workflow guide

[ganesh47]

Shipped in 5d31e4a and released in v0.13.0.

Completed:

• rewrote docs/specs/cstack-spec-v0.1.md as the active shipped contract
• aligned README.md and docs/workflows/current-project-workflow.md to the real command surface
• added the missing standalone command docs for review, ship, resume, fork, and rerun
• marked slice/design notes as historical where they are no longer the active contract
• documented explicit dirty-worktree consent for mutation-capable workflows

The active spec no longer promises unfinished workflow commands.