Track cmd/email-agent/main.go (fix .gitignore shadowing)

The unanchored `email-agent` ignore rule matched the `cmd/email-agent/`
directory as well as the root build artifact, so the service entry point was
never committed and a fresh clone could not build. Anchor the rule to the repo
root (`/email-agent`).

This completes the Phase 1.1 tracked tree (AUD-58): entry point, config, SQLite
store, HTTP server, Dockerfile and compose.

Co-Authored-By: Paperclip <noreply@paperclip.ing>

.gitignore

@@ -13,7 +13,8 @@ bin/
 
 # Local runtime data (SQLite)
 data/
-email-agent
+# Compiled binary at the repo root only. Must NOT match cmd/email-agent/.
+/email-agent
 
 # Python
 __pycache__/