docs: audit corrections, coverage pages, screenshots, and em-dash removal

Finalizes the docs section after an adversarial audit (code review + per-page
fact-check + coherence critic) and two content requests.

- Accuracy: fixed 10 invented cross-link slugs, the admin-vs-board gating claims
  the verifiers caught (permissions matrix, /settings, invites, onboarding,
  connect-payments, proposal withdraw, Stripe reconciliation, member fields,
  door.operate), and 2 issues in the new pages (project area-at-creation, forum
  thread-delete role).
- Coverage: added 5 how-to pages so every module is documented (recurring Stripe
  dues, tasks & chores, projects, comms & forum, ops knowledge base + secrets
  vault). 34 pages total.
- Screenshots: 12 captioned app screenshots under public/docs-media/, embedded
  as figures. Each tutorial now has 2-3 step screenshots.
- Style: removed all em-dashes/en-dashes/ellipses from the docs (natural ASCII
  punctuation).
- Handoff (docs/HANDOFF-audit-cleanup.md) updated with the current state.

typecheck 0 · lint 0 errors · build ok (all 34 /docs pages prerendered)

components/docs/docs-markdown.tsx

@@ -21,6 +21,17 @@ export function DocsMarkdown({ content }: { content: string }) {
           h2: ({ children }) => <h2 id={slug(children)}>{children}</h2>,
           h3: ({ children }) => <h3 id={slug(children)}>{children}</h3>,
           h4: ({ children }) => <h4 id={slug(children)}>{children}</h4>,
+          // Render images as captioned figures. Uses spans (valid inside the
+          // <p> react-markdown wraps a lone image in) styled as blocks; the alt
+          // text doubles as the caption.
+          img: ({ src, alt }) =>
+            typeof src === 'string' ? (
+              <span className="docs-figure">
+                {/* eslint-disable-next-line @next/next/no-img-element */}
+                <img src={src} alt={alt ?? ''} loading="lazy" />
+                {alt ? <span className="docs-figcaption">{alt}</span> : null}
+              </span>
+            ) : null,
           a: ({ href, children }) =>
             isInDocumentHref(href) ? (
               <a href={href}>{children}</a>