decomposer(preflight): judge a generated plan before contributors spend cycles on it

[JSONbored]

Problem

The gate judges PRs. Nothing judges the plan. A bad backlog is discovered only after
contributors have burned effort on it, and by then the cost is already paid.

Scope

• Pre-flight check over a generated plan, run before it is posted: criteria coverage
  (every blocking criterion mapped), issue sizing outliers, missing acceptance detail,
  dependency cycles, and orphaned issues mapping to no criterion
• Predicted issue-quality score per issue, using the model from Epic: issue-quality measurement — score a scoped issue by how cleanly it executed #10076 — flag issues
  scoring below a floor so they are rewritten rather than posted
• Report as a structured verdict the drafter can act on, not a pass/fail
• Advisory in v1: it informs the human approval step rather than blocking, until its own
  accuracy is established

Acceptance

A plan with an uncovered criterion, a dependency cycle, or an issue predicted to execute
badly is flagged before posting.

Depends on

#10076 (score), #10082 (coverage).

[linear-code]

JSO-7091