v0.7.1 — the docs catch up with the cap

A documentation-correctness release. v0.7.0 made the question cap negotiable — default 20,
or the number the user asked for — and updated the requirements that say so. It did not
update the prose that restates the old rule as an absolute, so the docs asserted both
versions at once. Two of the corrected files ship inside the installed plugin, and plugin
components are cached at install time, so this needs a version bump to reach anyone.
No behaviour change.

Fixed

• The docs now agree with the shipped cap. Eleven places across README.md,
  docs/design.md and SKILL.md's frontmatter still promised "no more than 20 questions"
  or a "hard maximum of 20 user-visible questions". The frontmatter matters most: it is the
  agent's matching surface, and it advertised capped (<=20) for a form that will carry 30
  if the user asks. Requirements FR-008, FR-046, NFR-002 and NFR-042 were already correct.
• web/README.md pointed at a directory that does not exist. Tests live in tests/ at
  the repository root, not web/test/, and the list named four of the seven suites.
• decision-matrix was missing from web/README.md's question-type list. v0.3.0 fixed
  exactly this omission in SKILL.md and added a guard against it recurring — but the guard
  only ever read SKILL.md, so the type stayed invisible here for four more releases. The
  guard now reads both files.
• web/README.md described security that v0.7.0 replaced. It still claimed the server
  checks only questionnaire.id; submissions are now checked for identity, shape and
  referential integrity before anything is written.
• docs/development.md miscounted the manifests (seven files carrying ten version
  fields, not six), omitted test-build, test-followup and the followup target, and had
  no row for docs/plan/.

Changed

• The README gallery no longer opens by repeating the hero screenshot. The single-select
  cell used the same image shown directly above it, and the boolean cell was redundant with
  the contradiction check, which is itself a yes/no question. Both types are still named in
  the surrounding captions; the grid is now 3x2.