Show subscribers on sequences (list count + subscriber list on the sequence page) #153

CourseLit, which SendLit was extracted from, shows who is in a sequence. SendLit doesn't, so there is no way to tell from the dashboard who a sequence is reaching.

CourseLit

• The sequences list has a Subscribers column (for example New users welcome: 1266, KYC: 795).
• The sequence's Analytics tab shows Subscribers, Emails sent, open rate, click rate and click-to-open, plus a Subscribers (N) table with each contact's avatar, name and email.

SendLit today

• The sequences list shows only Title, Status and Emails.
• The sequence page shows Sent, Recipients and rates, but has no subscriber list.
• GET /sequences/:sequenceId/subscribers exists, but it returns contact ids only and the web app doesn't use it.

Screenshots: SendLit on the left, CourseLit on the right (attached below).

Scope

• API: make /sequences/:sequenceId/subscribers return paginated contacts (name, email, contact id, enrolled at, current step, status: active / completed / exited). Add a subscribersCount to the sequence list response. Update the OpenAPI docs.
• MCP: expose the subscriber list and count in the sequences tools.
• Dashboard:
  • Add a Subscribers column to the sequences list.
  • Add a Subscribers stat and a paginated subscribers table (shadcn) on the sequence page. Each row links to the contact.
  • Use the Loading component while the table loads.
• Definitions: "Subscribers" means contacts enrolled in the sequence (ongoing_sequences plus those who completed it). Keep it separate from "Recipients", which is contacts that have received at least one email, so the two numbers don't conflict.
• Consider the same subscriber list for broadcasts (recipients).