Phase 16: hardening and release 0.1.0

- TOTP second factor (RFC 6238, secret encrypted under the master key),
  ten hashed single-use recovery codes, two-step login with a pending token
  bound to the client address, account enrolment/disable, admin reset
- tests/security: prompt-injection corpus never acts or creates evidence-free
  beliefs; roles and CSRF on form and API paths; cross-mind isolation
  (demo scenario 5); stored-XSS escaping and CSP across pages; secrets never
  echoed (API, pages, database, archives); hostile archive import; session
  lifecycle and security headers
- OpenAPI 3.1 document generated from the route table, served at
  /api/v1/openapi.json and kept complete by a test
- gosec clean (justified #nosec annotations, cookie/redirect hardening,
  bounded multipart parsing, UUID packing without narrowing conversions);
  govulncheck clean with toolchain pinned to go1.26.8
- THREAT_MODEL verification pointers, SECURITY.md testing section, README,
  CHANGELOG 0.1.0, docs/RELEASE_NOTES.md, PLAN status

web/templates/pages/users.html

@@ -18,7 +18,8 @@
         <td>{{if .TOTPEnabled}}<span class="badge ok">TOTP</span>{{else}}<span class="muted">off</span>{{end}}</td>
         <td class="muted small nowrap">{{date .CreatedAt}}</td>
         <td>{{if ne .ID $.Principal.User.ID}}<form method="post" action="/admin/users/{{.ID}}" class="inline"><input type="hidden" name="_csrf" value="{{$.CSRF}}">
-          {{if .Disabled}}<button class="btn small" name="action" value="enable">Enable</button>{{else}}<button class="btn small btn-danger" name="action" value="disable" data-confirm="Disable {{.Username}} and revoke their sessions?">Disable</button>{{end}}</form>{{end}}</td>
+          {{if .Disabled}}<button class="btn small" name="action" value="enable">Enable</button>{{else}}<button class="btn small btn-danger" name="action" value="disable" data-confirm="Disable {{.Username}} and revoke their sessions?">Disable</button>{{end}}
+          {{if .TOTPEnabled}}<button class="btn small" name="action" value="reset-totp" data-confirm="Remove {{.Username}}'s second factor and recovery codes? They should re-enrol.">Reset 2FA</button>{{end}}</form>{{end}}</td>
       </tr>{{end}}</tbody>
     </table>
   </div>