feat(gateway): confirmEmailLink RPC + language on the email request + profile event

Add the confirm-link edge method (auth.email.confirm_link): a new
EmailConfirmLinkRequest/Result fbs table, the transcode const + handler + encoder,
and the backend-client call to the existing /sessions/email/confirm-link endpoint —
it rides Execute under the existing service prefix, so no proto/Caddy change. Add a
language field to EmailRequestRequest and forward it (the backend already seeds it).
Add the NotifyProfile sub-kind + notify.ProfileChanged, published by the confirm-link
handler on a successful link so an in-app session re-fetches its profile when the
email was confirmed in another browser. Regenerated fbs bindings (Go + TS).

gateway/internal/transcode/encode.go

@@ -37,6 +37,35 @@ func encodeAck(ok bool) []byte {
 	return b.FinishedBytes()
 }
 
+// encodeConfirmLinkResult builds an EmailConfirmLinkResult payload, embedding the
+// minted Session for a login. All strings and the nested Session table are built
+// before the result table is opened.
+func encodeConfirmLinkResult(r backendclient.ConfirmLinkResp) []byte {
+	b := flatbuffers.NewBuilder(160)
+	purpose := b.CreateString(r.Purpose)
+	status := b.CreateString(r.Status)
+	var session flatbuffers.UOffsetT
+	if r.Session != nil {
+		token := b.CreateString(r.Session.Token)
+		uid := b.CreateString(r.Session.UserID)
+		name := b.CreateString(r.Session.DisplayName)
+		fb.SessionStart(b)
+		fb.SessionAddToken(b, token)
+		fb.SessionAddUserId(b, uid)
+		fb.SessionAddIsGuest(b, r.Session.IsGuest)
+		fb.SessionAddDisplayName(b, name)
+		session = fb.SessionEnd(b)
+	}
+	fb.EmailConfirmLinkResultStart(b)
+	fb.EmailConfirmLinkResultAddPurpose(b, purpose)
+	fb.EmailConfirmLinkResultAddStatus(b, status)
+	if r.Session != nil {
+		fb.EmailConfirmLinkResultAddSession(b, session)
+	}
+	b.Finish(fb.EmailConfirmLinkResultEnd(b))
+	return b.FinishedBytes()
+}
+
 // encodeProfile builds a Profile payload, including the advertising-banner block
 // when the backend marked the viewer eligible.
 func encodeProfile(p backendclient.ProfileResp) []byte {