Add yaw2 invite interoperability

Protocol:
- invite.go: include full 64-char `net` hash in waste: invite blob
  (matches yaw2's `net` field — any client parsing the base64 JSON can
  join without knowing the plaintext name). Expose NetHash() helper.
- netmgr: add JoinByHash() — join via full 64-char hex hash alone,
  storing the short ID as display name. Enables joining yaw2 networks
  from a URL that only carries the hash.
- anchor: expose RunByHash() so netmgr can pass a pre-computed hash
  directly without a name→hash roundtrip.
- ipc/proto: add network_hash field to join_network — routes to
  JoinByHash when present and network_name is absent.

Web UI:
- Parse ?net=<64hex> (yaw2 URL param) and ?a=<anchor> in addition to
  existing ?n= / ?invite= params. Hash-only joins send network_hash.
- Sidebar shows yaw: contact card (yaw:<masterID>?n=<alias>) using the
  master identity — compatible with yaw2 contact card format. Click to
  copy to clipboard.

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

internal/ipc/ipc.go

@@ -137,16 +137,25 @@ func handleClient(conn net.Conn, mgr *netmgr.Manager) {
 		switch cmd.Type {
 
 		case proto.CmdJoinNetwork:
-			if cmd.NetworkName == "" {
-				send(errMsg("join_network: network_name is required"))
+			var (
+				netID string
+				err   error
+			)
+			switch {
+			case cmd.NetworkName != "":
+				netID, err = mgr.Join(cmd.NetworkName, cmd.ShareDir)
+			case len(cmd.NetworkHash) == 64:
+				// yaw2-compatible: join by full 64-char hex hash (net field)
+				netID, err = mgr.JoinByHash(cmd.NetworkHash, cmd.ShareDir)
+			default:
+				send(errMsg("join_network: network_name or network_hash (64 hex chars) required"))
 				continue
 			}
-			netID, err := mgr.Join(cmd.NetworkName, cmd.ShareDir)
 			if err != nil {
 				send(errMsg(fmt.Sprintf("join_network: %v", err)))
 				continue
 			}
-			// network_joined event (with share_dir) is emitted by Manager.Join.
+			// network_joined event (with share_dir) is emitted by Manager.Join/JoinByHash.
 			_ = netID
 
 		case proto.CmdLeaveNetwork: