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>

test-tui.sh

@@ -77,15 +77,18 @@ ANCHOR_URL="ws://127.0.0.1:${ANCHOR_PORT}/ws"
 
 # Daemons
 "$DATA_ROOT/bin/waste-daemon" -alias alice -data-dir "$DATA_ROOT/alice" \
-    -ipc-port "$ALICE_IPC" -anchor "$ANCHOR_URL" 2>/dev/null &
+    -ipc-port "$ALICE_IPC" -anchor "$ANCHOR_URL" \
+    -share-dir "/home/frejoh/Downloads/alice" 2>/dev/null &
 PIDS+=($!)
 
 "$DATA_ROOT/bin/waste-daemon" -alias bob -data-dir "$DATA_ROOT/bob" \
-    -ipc-port "$BOB_IPC" -anchor "$ANCHOR_URL" 2>/dev/null &
+    -ipc-port "$BOB_IPC" -anchor "$ANCHOR_URL" \
+    -share-dir "/home/frejoh/Downloads/bob" 2>/dev/null &
 PIDS+=($!)
 
 "$DATA_ROOT/bin/waste-daemon" -alias charlie -data-dir "$DATA_ROOT/charlie" \
-    -ipc-port "$CHARLIE_IPC" -anchor "$ANCHOR_URL" 2>/dev/null &
+    -ipc-port "$CHARLIE_IPC" -anchor "$ANCHOR_URL" \
+    -share-dir "/home/frejoh/Downloads/charlie" 2>/dev/null &
 PIDS+=($!)
 
 wait_port "$ALICE_IPC"