feat(plan): yodel plan --part writes the versioned plan as a chant change-set part (#237)

[lex00]

Closes #237

yodel plan <env> --part <file> writes the versioned plan as a chant change-set part (planner sql), through the sql lexicon's sqlVersionedPlanPart (chant 0.124.23). A chant Op reads it with readChangeSetPart, joins it to other members' parts with composeChangeSet, and gates them together; a Cedar policy reads the result as context.plan.

• One entry per object the pending steps touch, action and disruption from the change classes; steps a partial run already applied are left out; statements redacted as in --json.
• The member's plan digest is yodel's, the one yodel apply's gate binds. A plan apply would refuse is a failed member.
• Refused on a declarative project and on a tenant set (plan one tenant).
• src/pr/part.ts, the flag in src/commands/plan.ts.
• docs/approval.md: a section with an Op that composes the part with a Terraform plan, and a Cedar rule over it.
• test/plan-part.test.ts: the entries, the digest, redaction, chant reading the JSON back and composing it, a refused plan. test/pr-cli.test.ts: the declarative refusal.
• The approval claim's approval part writes the part against the server and checks chant reads it back as planned under the gate's digest. npm run claims -- approval on this branch: ch and pg pass, both caught under BREAK=1.