feat: persistent multi-share configuration (shares.json + localStorage)

Daemon side:
- internal/shares: new package reads/writes shares.json next to identity
- proto: add ShareEntry type, add_share/remove_share/list_shares IPC commands,
  shares_list event, path field on FileEntry
- netmgr: load shares.json on startup; ScanAllShares combines legacy ShareDir
  with shares.json entries (recursive walk with relative paths)
- mesh: ScanFiles callback lets manager inject multi-share scanning without
  mesh knowing about shares.json
- ipc: handle add_share, remove_share, list_shares commands

Browser side:
- ShareManager component replaces FolderPicker: shows list of named shares
  with remove/re-pick buttons; persists share records to waste_shares in
  localStorage (name, global flag, networkId)
- FolderPicker retained for internal use; Sidebar now uses ShareManager

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

internal/proto/proto.go

@@ -111,6 +111,13 @@ type GossipEntry struct {
 type FileEntry struct {
 	Name      string `json:"name"`
 	SizeBytes int64  `json:"size_bytes"`
+	Path      string `json:"path,omitempty"` // relative path including filename
+}
+
+// ShareEntry describes one persistent share root.
+type ShareEntry struct {
+	Path     string   `json:"path"`
+	Networks []string `json:"networks"` // ["*"] = global
 }
 
 // FileListResp is the payload for MsgFileListResp.
@@ -222,6 +229,9 @@ const (
 	CmdGetFileList    IpcMsgType = "get_file_list"
 	CmdExportIdentity IpcMsgType = "export_identity"  // returns encrypted backup blob
 	CmdImportIdentity IpcMsgType = "import_identity"  // replaces identity from backup blob
+	CmdAddShare       IpcMsgType = "add_share"        // add a share root; fields: path, networks
+	CmdRemoveShare    IpcMsgType = "remove_share"      // remove a share root; field: path
+	CmdListShares     IpcMsgType = "list_shares"       // returns shares_list event
 
 	// Events (daemon → UI)
 	EvtMessageReceived  IpcMsgType = "message_received"
@@ -240,6 +250,7 @@ const (
 	EvtNetworkLeft      IpcMsgType = "network_left"
 	EvtIdentityExported IpcMsgType = "identity_exported"
 	EvtIdentityImported IpcMsgType = "identity_imported"
+	EvtSharesList       IpcMsgType = "shares_list"
 )
 
 // NetworkInfo summarises one joined network for state_snapshot and network_joined events.
@@ -292,6 +303,8 @@ type IpcMessage struct {
 	ErrorMessage   string       `json:"error_message,omitempty"`
 	InviteString   string       `json:"invite,omitempty"`
 	Files          []FileEntry  `json:"files,omitempty"`
+	Shares         []ShareEntry `json:"shares,omitempty"`
+	ShareNetworks  []string     `json:"networks,omitempty"` // for add_share command
 	// export_identity / import_identity
 	Passphrase     string       `json:"passphrase,omitempty"` // import only; never echoed back
 	Backup         string       `json:"backup,omitempty"`     // JSON backup blob