decomposer(intake): brief + clarifying loop into a structured intent record

[JSONbored]

Problem

A brief from someone who is not the maintainer will be underspecified in ways the author
does not notice. Decomposing it directly produces a confident, wrong backlog.

Scope

• Intake that accepts free-text and returns targeted clarifying questions, ending in a
  structured intent record: goal, in-scope, explicitly out-of-scope, constraints (language,
  runtime, deployment target), and the definition of success in the submitter's own words
• Ask only about ambiguities that would change the backlog — question volume is a cost, and
  a submitter who abandons intake is worse than a slightly underspecified plan
• Record the unresolved ambiguities that intake could not settle, so downstream steps and
  the operator can see what was assumed
• Feed the intent record into acceptance-criteria generation (apr(completion): acceptance-criteria record — format, customer approval, immutability after work starts #10081)

Acceptance

A vague one-paragraph brief becomes an intent record a third party could decompose from,
with unresolved assumptions listed rather than silently invented.

Out of scope

Generating the backlog (sibling).

[linear-code]

JSO-7089