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/netmgr/manager.go

@@ -10,6 +10,7 @@ import (
 	"encoding/hex"
 	"fmt"
 	"log"
+	"os"
 	"path/filepath"
 	"sync"
 
@@ -17,6 +18,7 @@ import (
 	"github.com/waste-go/internal/crypto"
 	"github.com/waste-go/internal/mesh"
 	"github.com/waste-go/internal/proto"
+	"github.com/waste-go/internal/shares"
 	"github.com/waste-go/internal/store"
 )
 
@@ -54,13 +56,22 @@ type Manager struct {
 
 	subsMu sync.Mutex
 	subs   []chan proto.IpcMessage
+
+	Shares *shares.Store // persistent multi-share configuration
 }
 
 // New creates a Manager from the given config.
+// Loads shares.json from StoreDir if it exists.
 func New(cfg Config) *Manager {
+	sh, err := shares.Load(cfg.StoreDir)
+	if err != nil {
+		log.Printf("netmgr: loading shares.json: %v (starting empty)", err)
+		sh, _ = shares.Load("") // fallback to empty
+	}
 	return &Manager{
 		networks: make(map[string]*Network),
 		cfg:      cfg,
+		Shares:   sh,
 	}
 }
 
@@ -100,6 +111,8 @@ func (mgr *Manager) Join(name, shareDir string) (string, error) {
 		m.ShareDir = mgr.cfg.ShareDir
 	}
 	m.DownloadDir = filepath.Join(mgr.cfg.StoreDir, "downloads-"+netID_full)
+	capturedNetID := netID
+	m.ScanFiles = func() []proto.FileEntry { return mgr.ScanAllShares(capturedNetID) }
 
 	// Forward all mesh events to the Manager's fan-out, tagging with network_id.
 	meshEvents := m.Subscribe()
@@ -183,6 +196,8 @@ func (mgr *Manager) JoinByHash(netHash64, shareDir string) (string, error) {
 		m.ShareDir = mgr.cfg.ShareDir
 	}
 	m.DownloadDir = filepath.Join(mgr.cfg.StoreDir, "downloads-"+netID)
+	capturedNetID2 := netID
+	m.ScanFiles = func() []proto.FileEntry { return mgr.ScanAllShares(capturedNetID2) }
 
 	meshEvents := m.Subscribe()
 	go func() {
@@ -313,6 +328,50 @@ func (mgr *Manager) All() []*Network {
 	return out
 }
 
+// ScanAllShares returns file entries from all share roots visible to networkID,
+// combining the network's legacy ShareDir with entries from shares.json.
+func (mgr *Manager) ScanAllShares(netID string) []proto.FileEntry {
+	var files []proto.FileEntry
+
+	// Legacy single-dir share from the network mesh.
+	if n := mgr.Resolve(netID); n != nil {
+		files = append(files, n.Mesh.ScanShareDir()...)
+	}
+
+	// Additional shares from shares.json.
+	if mgr.Shares != nil {
+		for _, sh := range mgr.Shares.ForNetwork(netID) {
+			files = append(files, scanDir(sh.Path)...)
+		}
+	}
+	return files
+}
+
+// scanDir recursively walks a directory and returns FileEntry for each file.
+func scanDir(root string) []proto.FileEntry {
+	var files []proto.FileEntry
+	_ = filepath.WalkDir(root, func(path string, d os.DirEntry, err error) error {
+		if err != nil || d.IsDir() {
+			return nil
+		}
+		info, err := d.Info()
+		if err != nil {
+			return nil
+		}
+		rel, err := filepath.Rel(root, path)
+		if err != nil {
+			rel = d.Name()
+		}
+		files = append(files, proto.FileEntry{
+			Name:      d.Name(),
+			SizeBytes: info.Size(),
+			Path:      rel,
+		})
+		return nil
+	})
+	return files
+}
+
 // AnchorURL returns the configured anchor URL.
 func (mgr *Manager) AnchorURL() string { return mgr.cfg.AnchorURL }