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

internal/auth/password.go

@@ -63,7 +63,7 @@ func VerifyPassword(hash, password string) (bool, error) {
 	if err != nil {
 		return false, err
 	}
-	got := argon2.IDKey([]byte(password), salt, t, m, p, uint32(len(want)))
+	got := argon2.IDKey([]byte(password), salt, t, m, p, uint32(len(want))) // #nosec G115 -- key length is 32
 	return subtle.ConstantTimeCompare(got, want) == 1, nil
 }