Multi-network foundation: netmgr, derived identities, additive IPC protocol

YAW/2 peer wire protocol is unchanged. Changes are local only.

internal/crypto:
- DeriveForNetwork(master, networkHash) — HKDF-SHA256 from master seed + network hash;
  same master + same network always produces the same Ed25519 keypair (stable peer ID)

internal/proto:
- NetworkInfo type (network_id, network_name, local_peer)
- NetworkID field on IpcMessage (optional; commands default to first network when absent)
- Networks []NetworkInfo on state_snapshot (additive alongside existing local_peer)
- EvtNetworkJoined / EvtNetworkLeft events

internal/netmgr (new):
- Manager holds N independent Network contexts (derived identity, mesh, store, anchor)
- Join(name) creates context, derives identity, opens per-network DB, starts anchor client
- Leave(id) / LeaveAll() cancel contexts and close stores
- Resolve(netID) returns named network, or Default() when netID is empty (backward compat)
- Fan-out: Manager.Subscribe() receives tagged events from all networks
- Network IDs are the first 8 hex chars of SHA-256("yaw2-net:"+name) — stable and short

internal/ipc:
- Run(mgr, port) replaces Run(m *mesh.Mesh, port, anchorURL, joinFn)
- Commands without network_id route to mgr.Default() (backward compat)
- state_snapshot includes Networks array; local_peer/connected_peers still populated from first network
- generate_invite, get_file_list, send_message all respect network_id routing

cmd/daemon:
- Creates netmgr.Manager instead of mesh.Mesh directly
- --join and --share-dir pass through Config
- Auto-join via mgr.Join() before IPC starts

test-network.sh:
- Fix peer_name bash bug: $() with && inside triggers set -e; use if/elif/else instead

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/proto/proto.go

@@ -215,12 +215,25 @@ const (
 	EvtError            IpcMsgType = "error"
 	EvtInviteGenerated  IpcMsgType = "invite_generated"
 	EvtFileList         IpcMsgType = "file_list"
+	EvtNetworkJoined    IpcMsgType = "network_joined"
+	EvtNetworkLeft      IpcMsgType = "network_left"
 )
 
+// NetworkInfo summarises one joined network for state_snapshot and network_joined events.
+type NetworkInfo struct {
+	NetworkID   string    `json:"network_id"`
+	NetworkName string    `json:"network_name"`
+	LocalPeer   *PeerInfo `json:"local_peer,omitempty"`
+}
+
 // IpcMessage covers both commands and events.
 type IpcMessage struct {
 	Type IpcMsgType `json:"type"`
 
+	// optional: scopes a command/event to a specific network.
+	// When absent, defaults to the first (or only) joined network.
+	NetworkID string `json:"network_id,omitempty"`
+
 	// send_message
 	Room string  `json:"room,omitempty"`
 	To   *PeerID `json:"to,omitempty"`
@@ -241,9 +254,12 @@ type IpcMessage struct {
 	TransferID     string       `json:"transfer_id,omitempty"`
 	BytesReceived  int64        `json:"bytes_received,omitempty"`
 	TotalBytes     int64        `json:"total_bytes,omitempty"`
-	LocalPeer      *PeerInfo    `json:"local_peer,omitempty"`
-	ConnectedPeers []PeerInfo   `json:"connected_peers,omitempty"`
-	Rooms          []string     `json:"rooms,omitempty"`
+	// state_snapshot fields (existing shape preserved for backward compat)
+	LocalPeer      *PeerInfo     `json:"local_peer,omitempty"`
+	ConnectedPeers []PeerInfo    `json:"connected_peers,omitempty"`
+	Rooms          []string      `json:"rooms,omitempty"`
+	// multi-network: all joined networks (additive)
+	Networks       []NetworkInfo `json:"networks,omitempty"`
 	ErrorMessage   string       `json:"error_message,omitempty"`
 	InviteString   string       `json:"invite,omitempty"`
 	Files          []FileEntry  `json:"files,omitempty"`