Stage 11: account linking & merge (email + Telegram Login Widget)

Link an email (confirm-code) or Telegram (web Login Widget) to the current
account; if the identity already has its own account, merge the two into the
one in use (the current account is primary, except a guest initiator whose
durable counterpart wins). The merge runs in one transaction
(internal/accountmerge): stats + hint wallet summed, paid_account ORed,
identities/games/chat/complaints transferred, friends/blocks de-duplicated,
the secondary kept as a merged_into tombstone so a shared finished game's
no-cascade FKs hold; a shared active game blocks the merge.

- migration 00009: accounts.paid_account, merged_into, merged_at (+ jetgen)
- internal/link orchestrator; session.RevokeAllForAccount on merge
- connector ValidateLoginWidget RPC + loginwidget HMAC validator
- edge ops link.email.request/confirm/merge, link.telegram.confirm/merge;
  supersedes the Stage 8 email.bind.* surface (request never reveals 'taken'
  before the code is verified, so a probe cannot enumerate addresses)
- UI Profile link section + irreversible-merge dialog; Telegram web sign-in
- focused regression tests (merge core, guest inversion, active-game refusal,
  finished-shared-game kept), gateway transcode + connector + UI codec/e2e
- docs: PLAN, ARCHITECTURE 3/4/9, FUNCTIONAL(+ru), module READMEs

platform/telegram/internal/loginwidget/validator_test.go

@@ -0,0 +1,98 @@
+package loginwidget
+
+import (
+	"crypto/hmac"
+	"crypto/sha256"
+	"encoding/hex"
+	"errors"
+	"net/url"
+	"sort"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+)
+
+const testToken = "123456:TESTTOKEN"
+
+// signWidget builds validly signed Login Widget data for the token and fields,
+// mirroring Telegram's algorithm (secret = SHA-256(token); HMAC over the sorted
+// data-check string).
+func signWidget(token string, fields map[string]string) string {
+	keys := make([]string, 0, len(fields))
+	for k := range fields {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+	lines := make([]string, 0, len(keys))
+	for _, k := range keys {
+		lines = append(lines, k+"="+fields[k])
+	}
+	secret := sha256.Sum256([]byte(token))
+	mac := hmac.New(sha256.New, secret[:])
+	mac.Write([]byte(strings.Join(lines, "\n")))
+
+	v := url.Values{}
+	for k, val := range fields {
+		v.Set(k, val)
+	}
+	v.Set("hash", hex.EncodeToString(mac.Sum(nil)))
+	return v.Encode()
+}
+
+func freshFields() map[string]string {
+	return map[string]string{
+		"auth_date":  strconv.FormatInt(time.Now().Unix(), 10),
+		"id":         "42",
+		"username":   "neo",
+		"first_name": "Thomas",
+	}
+}
+
+func TestValidateOK(t *testing.T) {
+	data := signWidget(testToken, freshFields())
+	u, err := NewHMACValidator(testToken).Validate(data)
+	if err != nil {
+		t.Fatalf("validate: %v", err)
+	}
+	if u.ExternalID != "42" || u.Username != "neo" || u.FirstName != "Thomas" {
+		t.Errorf("user = %+v, want {42 neo Thomas}", u)
+	}
+}
+
+func TestValidateRejects(t *testing.T) {
+	valid := signWidget(testToken, freshFields())
+
+	t.Run("tampered hash", func(t *testing.T) {
+		tampered := strings.Replace(valid, "hash=", "hash=00", 1)
+		if _, err := NewHMACValidator(testToken).Validate(tampered); !errors.Is(err, ErrInvalidLoginWidget) {
+			t.Errorf("err = %v, want ErrInvalidLoginWidget", err)
+		}
+	})
+	t.Run("wrong token", func(t *testing.T) {
+		if _, err := NewHMACValidator("other:TOKEN").Validate(valid); !errors.Is(err, ErrInvalidLoginWidget) {
+			t.Errorf("err = %v, want ErrInvalidLoginWidget", err)
+		}
+	})
+	t.Run("tampered field", func(t *testing.T) {
+		// Flip the id after signing: the HMAC must no longer match.
+		forged := strings.Replace(valid, "id=42", "id=43", 1)
+		if _, err := NewHMACValidator(testToken).Validate(forged); !errors.Is(err, ErrInvalidLoginWidget) {
+			t.Errorf("err = %v, want ErrInvalidLoginWidget", err)
+		}
+	})
+	t.Run("missing hash", func(t *testing.T) {
+		if _, err := NewHMACValidator(testToken).Validate("id=42&auth_date=1"); !errors.Is(err, ErrInvalidLoginWidget) {
+			t.Errorf("err = %v, want ErrInvalidLoginWidget", err)
+		}
+	})
+	t.Run("stale auth_date", func(t *testing.T) {
+		stale := signWidget(testToken, map[string]string{
+			"auth_date": strconv.FormatInt(time.Now().Add(-48*time.Hour).Unix(), 10),
+			"id":        "42",
+		})
+		if _, err := NewHMACValidator(testToken).Validate(stale); !errors.Is(err, ErrInvalidLoginWidget) {
+			t.Errorf("err = %v, want ErrInvalidLoginWidget", err)
+		}
+	})
+}