feat(skills): add ChatGPT-authored /ship planning

[BorisTyshkevich]

What & why

Add an opt-in /ship <scope> --planner chatgpt workflow while preserving the existing Fable-authored path as the default.

ChatGPT can now privately author and revise complete standalone plans through a strict READY/BLOCKED protocol. Valid plans atomically replace the canonical plan file; malformed, empty, blocked, or incomplete responses leave the previous plan untouched. Fable/high remains the final plan approver, and Sonnet agents verify each substantive review finding.

The implementation also documents the workflow, adds deterministic invocation parsing, preserves same-conversation and pass-numbered upload behavior, and keeps plan authoring unable to publish GitHub comments or perform other external writes.

Checklist

• npm test passes (the per-file coverage gate is non-negotiable)
• Tests added/updated in the same change as the code
• npm run build succeeds (single-file dist/sql.html)
• Layers kept honest: this change is confined to skill tooling and documentation
• No new runtime dependency
• README / CHANGELOG.md ([Unreleased]) updated
• No application roadmap or ADR behavior was reshaped

Validation

• Full repository gate: types, architecture, schemas, examples, npm test, and build
• Repository coverage: 100% statements/functions/lines, 97.14% branches
• chatgpt-review: 36 tests
• /ship invocation and workflow contracts: 5 tests
• Both skill validators
• git diff --check