license: relicense to AGPL-3.0-only with commercial dual-license

- LICENSE -> verbatim GNU AGPL-3.0; add LICENSE-COMMERCIAL.md + SECURITY.md
- CLA -> exclusive-license grant (contributors keep copyright); add README
  anti-rugpull covenant + relicense record
- NOTICE / README / CONTRIBUTING / CLAUDE.md / package.json x5 updated;
  contact routed through GitHub (no email placeholders)
- AGPL section 13 source offer: operator-configurable BACKSPACE_SOURCE_URL +
  build-injected commit; sourceCodeUrl+commit on /api/instance/info;
  SourceCodeLink on login/register/settings/desktop; docs + .env.example updated

packages/web/src/components/auth/RegisterPage.tsx

@@ -9,6 +9,7 @@ import type { AvatarColor, CheckInviteResponse, InstanceInfoResponse } from '@ba
 import { api, RateLimitError } from '../../api/client';
 import { useTransferStore } from '../../stores/transferStore';
 import { waitForTransferAttachment } from '../../utils/waitForTransfer';
+import { SourceCodeLink } from '../ui/SourceCodeLink';
 
 // Single-source regex for extracting a bare invite token from a pasted full URL.
 // Token format: 22 chars base64url ([A-Za-z0-9_-]).
@@ -727,6 +728,13 @@ export function RegisterPage() {
             </div>
           </div>
         )}
+
+        {/* AGPL § 13: source offer for anonymous visitors, shown on both steps. */}
+        {instanceInfo && (
+          <div className="mt-6 pt-4 border-t border-white/[0.04] flex justify-center">
+            <SourceCodeLink sourceCodeUrl={instanceInfo.sourceCodeUrl} version={instanceInfo.version} commit={instanceInfo.commit} />
+          </div>
+        )}
         </div>
       </div>