Move email types to pkg/email for cloud repo access

Extracts Mailer interface, EmailData, and Button to pkg/email/types.go
so the cloud repo can use them via ServerContext. internal/email re-exports
the types as aliases so existing callers are unchanged. Also fixes
pre-existing lint errors (unchecked rollback and deadline calls).

internal/api/middleware_auth.go

@@ -96,4 +96,4 @@ func requireAPIKeyOrJWT(queries *db.Queries, jwtSecret []byte) func(http.Handler
 			writeError(w, http.StatusUnauthorized, "unauthorized", "X-API-Key or Authorization: Bearer <token> required")
 		})
 	}
-}
+}