flow-next v3.7.0

Changed

• Project-added spec sections are now first-class to the interview passes.
  flowctl scope write-policy enumerates the seven canonical sections only, so
  a section a project added via its own repo-root SPEC.md scaffold appeared in
  neither its writable nor its preserved list. The interview prose asked the
  agent to think in terms of that closed list, which left custom sections with
  no stated protection and no route to ever being filled. Ownership now comes
  from the section's own scope-owner marker in the spec body, with a three-way
  rule: a marker naming this pass's scope makes the section writable (filled
  and refined like a canonical section), a marker naming the other scope
  preserves it byte-for-byte, and no marker (or an unparseable one) preserves it
  byte-for-byte and says so in the read-back. scope: both is writable under
  any pass. Absence from the write-policy lists is explicitly never permission
  to drop a section. Scope-owner markers, previously strippable as authoring
  guidance, must now be kept on project-added sections because for those the
  marker is the only ownership signal a later pass has. Prose only - no
  flowctl change, no new command surface, no version bump.

Documentation

• Customizing the spec scaffold is now properly documented. The repo-root
  SPEC.md override has always won the 4-tier discovery cascade, but it was
  documented only as a lookup order - so the most useful thing about it, that a
  project can impose its own spec shape without forking the plugin, was easy to
  miss. plugins/flow-next/docs/spec-template.md gains a "Customizing the
  scaffold for your project" guide: how to do it, what is free to change
  (adding sections, reordering, rewriting the guidance prose under any
  heading), and a verified table of what silently degrades if you rename or
  remove ## Acceptance Criteria, ## Boundaries, ## Goal & Context or
  ## Decision Context. Also documents a known limitation: flowctl scope write-policy enumerates only the seven canonical sections, so a
  user-added section has no contractual byte-for-byte preservation guarantee
  under an interview pass (capture and plan are unaffected). The bundled
  template and CLAUDE.md cross-link the guide. Docs only - no behavior
  change, no version bump.