worker: stop polluting Resend dashboard with source as firstName

The firstName-as-source-tag hack was leaving 'website' / 'extension-setup'
in the dashboard's First Name column, which is uglier than just leaving
the field blank. We don't actually use signup-source for anything yet
(YAGNI). If we need it later, do it properly via a Resend Segment.

The route still accepts source for validation; we just don't pass it
through to Resend anymore.

Author: spencerc99

extension/worker/src/__tests__/resend.test.ts

@@ -42,11 +42,13 @@ describe('createResendClient', () => {
       expect.objectContaining({
         email: 'a@b.com',
         unsubscribed: false,
-        firstName: 'website',
       }),
     );
     const createCall = mockContactsCreate.mock.calls[0][0];
     expect(createCall.segments).toBeUndefined();
+    // We deliberately do NOT pass firstName — we'd be polluting the dashboard
+    // with the source value otherwise (custom properties are paid).
+    expect(createCall.firstName).toBeUndefined();
   });
 
   it('addContact passes segmentId via segments array when configured', async () => {
@@ -65,7 +67,6 @@ describe('createResendClient', () => {
     expect(mockContactsCreate).toHaveBeenCalledWith(
       expect.objectContaining({
         email: 'a@b.com',
-        firstName: 'extension-setup',
         segments: [{ id: 'seg_xyz' }],
       }),
     );

extension/worker/src/lib/resend.ts

@@ -56,15 +56,15 @@ export function createResendClient(config: ResendClientConfig): ResendClient {
         throw new Error(getError.message);
       }
 
+      // We accept `source` from callers but don't pass it to Resend — custom
+      // contact properties are a paid feature, and using firstName as a tag
+      // pollutes the dashboard. If we ever need to segment by signup source,
+      // do it via a proper Resend Segment.
+      void source;
+
       const { error: createError } = await resend.contacts.create({
         email,
         unsubscribed: false,
-        // Tag contact source via firstName so it shows up in the dashboard
-        // without needing custom contact properties (which are a paid feature
-        // on Resend). TODO: swap to proper metadata/tags once available on
-        // the free tier — note that this means dashboard 'first name' shows
-        // 'website' or 'extension-setup', not a real name.
-        firstName: source,
         ...(config.segmentId
           ? { segments: [{ id: config.segmentId }] }
           : {}),