fix(signing): branded embed URL for developer + Copy link

Two bugs in the marketing-site embed-URL rewrite, both surfaced by
testing through the actual invitation emails:

1. Developer invite linked to `…/sign/undefined/<token>`. document_signers
   persists Documenso's normalized role, so the order-2 EOI developer
   arrives as 'signer', which ROLE_TO_URL_SEGMENT didn't have — the lookup
   returned undefined. Add a 'signer' → 'developer' alias and a 'cc'
   fallback so an unknown role can never emit `/sign/undefined/`.

2. "Copy link" copied the bare Documenso URL, not the branded embed URL.
   listDocumentSigners (feeds the EOI tab signers + Copy link) now runs
   each signing_url through transformSigningUrl, so the copied link
   matches what the invitation email sends. Send-invitation/automation
   read the raw rows directly, so they're unaffected.

Regression tests pin 'signer' → /sign/developer and the unknown-role
fallback.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/unit/services/document-signing-urls.test.ts

@@ -44,6 +44,21 @@ describe('transformSigningUrl', () => {
     );
   });
 
+  it("maps 'signer' (Documenso's persisted order-2 role) → /sign/developer/<token>", () => {
+    // document_signers.signer_role stores Documenso's normalized role, so the
+    // EOI developer arrives as 'signer'. Regression: this used to fall through
+    // to `undefined` → dead `…/sign/undefined/<token>` invitation links.
+    expect(transformSigningUrl(RAW, HOST, 'signer' as never)).toBe(
+      'https://portnimara.com/sign/developer/vbT8hi3jKQmrFP_LN1WcS',
+    );
+  });
+
+  it('falls back to /sign/cc/<token> for any unrecognised role (never undefined)', () => {
+    expect(transformSigningUrl(RAW, HOST, 'mystery-role' as never)).toBe(
+      'https://portnimara.com/sign/cc/vbT8hi3jKQmrFP_LN1WcS',
+    );
+  });
+
   it('maps witness → /sign/witness/<token>', () => {
     expect(transformSigningUrl(RAW, HOST, 'witness')).toBe(
       'https://portnimara.com/sign/witness/vbT8hi3jKQmrFP_LN1WcS',