Add file listing: share-dir flag, file_list_req/resp DataChannel messages

- proto: FileEntry, FileListResp types; MsgFileListReq/Resp msg types;
  CmdGetFileList + EvtFileList IPC types; Files field on IpcMessage
- mesh: ShareDir field + ScanShareDir(); on DataChannel open, auto-send
  MsgFileListReq to new peer; handle MsgFileListReq (scan + reply) and
  MsgFileListResp (emit EvtFileList to IPC subscribers)
- ipc: get_file_list command — own list returned immediately; remote peer
  list requested via DataChannel (response arrives as EvtFileList event)
- daemon: -share-dir flag wired to mesh.ShareDir
- test scripts: pass -share-dir /home/frejoh/Downloads/{alice,bob,charlie};
  test-network.sh verifies each peer's own file list via get_file_list
- FUTURE.md: document per-network share directories and multi-network design

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

cmd/daemon/main.go

@@ -19,10 +19,11 @@ import (
 )
 
 func main() {
-	dataDir   := flag.String("data-dir", "~/.waste", "path to identity/config directory")
-	alias     := flag.String("alias", "anon", "display name shown to peers (advisory only)")
-	ipcPort   := flag.Int("ipc-port", 17337, "port for local IPC (UI connects here)")
-	anchorURL := flag.String("anchor", "", "anchor WebSocket URL, e.g. ws://your-vps:17339/ws")
+	dataDir    := flag.String("data-dir", "~/.waste", "path to identity/config directory")
+	alias      := flag.String("alias", "anon", "display name shown to peers (advisory only)")
+	ipcPort    := flag.Int("ipc-port", 17337, "port for local IPC (UI connects here)")
+	anchorURL  := flag.String("anchor", "", "anchor WebSocket URL, e.g. ws://your-vps:17339/ws")
+	shareDir   := flag.String("share-dir", "", "directory to share with peers on the network")
 	joinInvite := flag.String("join", "", "waste: invite string — sets anchor URL and auto-joins the network on startup")
 	flag.Parse()
 
@@ -52,6 +53,10 @@ func main() {
 	defer st.Close()
 
 	m := mesh.New(id, st)
+	if *shareDir != "" {
+		m.ShareDir = expandHome(*shareDir)
+		log.Printf("daemon: sharing %s", m.ShareDir)
+	}
 
 	// joinFn is passed to the IPC layer; it's called when the UI sends join_network.
 	joinFn := func(ctx context.Context, networkName string) {