multi: add version to models.ChannelEdgeInfo

And set it to V1 version everywhere.

Add a Version field to ChannelEdgeInfo to distinguish between v1 and
v2 channel announcements. Set it to GossipVersion1 for all existing
channels.

Both KV and SQL stores now validate that only v1 channels are
currently supported, returning an error for v2 channels. The KV store
automatically sets version to v1 when deserializing (since all
persisted channels in KV format are v1).

This versioning is essential for handling the different field
requirements and validation logic between v1 and v2 channels.

graph/db/sql_store.go

@@ -2038,7 +2038,9 @@ func (s *SQLStore) FetchChannelEdgesByID(chanID uint64) (
 			// populate the edge info with the public keys of each
 			// party as this is the only information we have about
 			// it.
-			edge = &models.ChannelEdgeInfo{}
+			edge = &models.ChannelEdgeInfo{
+				Version: lnwire.GossipVersion1,
+			}
 			copy(edge.NodeKey1Bytes[:], zombie.NodeKey1)
 			copy(edge.NodeKey2Bytes[:], zombie.NodeKey2)
 
@@ -4241,6 +4243,12 @@ func insertChannel(ctx context.Context, db SQLQueries,
 
 	v := lnwire.GossipVersion1
 
+	// For now, we only support V1 channel edges in the SQL store.
+	if edge.Version != v {
+		return fmt.Errorf("only V1 channel edges supported, got V%d",
+			edge.Version)
+	}
+
 	// Make sure that at least a "shell" entry for each node is present in
 	// the nodes table.
 	node1DBID, err := maybeCreateShellNode(
@@ -4458,6 +4466,7 @@ func buildEdgeInfoWithBatchData(chain chainhash.Hash,
 	copy(btcKey2[:], dbChan.BitcoinKey2)
 
 	channel := &models.ChannelEdgeInfo{
+		Version:          lnwire.GossipVersion1,
 		ChainHash:        chain,
 		ChannelID:        byteOrder.Uint64(dbChan.Scid),
 		NodeKey1Bytes:    node1,