fix(telegram): handle group-to-supergroup migration seamlessly

When a Telegram group upgrades to a supergroup, the chat ID changes and
all existing references become stale. This caused send failures (400),
orphaned sessions, and required manual re-pairing.

Add dual-path migration handling:
- Proactive: intercept inbound MigrateToChatID before isServiceMessage
- Reactive: detect 400 + MigrateToChatID on send, migrate DB, retry

DB migration updates in a single transaction (scoped by tenant + channel):
- paired_devices: sender_id, chat_id
- sessions: session_key, user_id
- channel_contacts: sender_id
- channel_pending_messages: history_key

Also invalidates in-memory caches (approvedGroups, pairingReplySent,
groupHistory) and handles media sends via migration retry in Send().

internal/http/auth_test.go

@@ -139,6 +139,9 @@ func (m *mockPairingStore) IsPaired(_ context.Context, senderID, channel string)
 }
 func (m *mockPairingStore) ListPending(context.Context) []store.PairingRequestData { return nil }
 func (m *mockPairingStore) ListPaired(context.Context) []store.PairedDeviceData    { return nil }
+func (m *mockPairingStore) MigrateGroupChatID(context.Context, string, string, string) error {
+	return nil
+}
 
 func TestResolveAuth_GatewayToken(t *testing.T) {
 	setupTestCache(t, nil)