[Backend] land sender/domain list endpoints and show them in the dash #265

Description

dash#94 / dash PR #98 lets people register senders and verify a domain, but the dash still can't answer "what can I send from?" because the gateway has no way to list them. The email controller only has POST /register-sender, /register-domain, /verify-domain and /send. The good news is David already built it last semester and it just never got reviewed. juno#251 adds getSenders/getDomains across proto, the email service and the gateway with green CI, and juno-sdk#75 adds the matching SDK methods with tests. This ticket is getting those two over the line and then wiring tables into the email configurations page from dash#94.

Rebase juno#251 onto main (it's from April and touches email.proto, so expect regen conflicts), get it reviewed and merged, and cut a release so the SDK can pick it up. Then land juno-sdk#75 and show a senders table and a domains table (with verified status) on /projects/[id]/services/email/configurations.

Acceptance Criteria

• juno#251 rebased, reviewed and merged, and GET senders/domains for a project work through the gateway with e2e tests
• juno-sdk#75 merged (or redone on top of the generated SDK) and released
• The email configurations page shows senders and domains tables that refresh after registering one
• Domain rows show verified vs pending, and you can re-run verify from the row
• Endpoints are scoped to the caller's project (JWT + x-project-id like the other routes), so one project can't list another's senders

Other Notes

Mid. Touches juno + juno-sdk + juno-dashboard.

• Supersedes [Spring 2026] Email Sender and Domain table #249 and dash PR #85, which were the older version of this. Close those once this lands.
• Delete is nice-to-have, not required.
• Christopher (Able Alliance) is the first real user who needs this, so test with a real from-address if you can.