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>

web/src/types.ts

@@ -32,6 +32,11 @@ export interface FileEntry {
   path?: string  // relative path including filename, e.g. "docs/report.pdf"
 }
 
+export interface ShareEntry {
+  path: string
+  networks: string[]  // ["*"] = global
+}
+
 export interface FileOffer {
   xid: string
   name: string
@@ -56,6 +61,9 @@ export type IpcMsgType =
   | 'get_file_list'
   | 'export_identity'
   | 'import_identity'
+  | 'add_share'
+  | 'remove_share'
+  | 'list_shares'
   // events
   | 'state_snapshot'
   | 'message_received'
@@ -71,6 +79,7 @@ export type IpcMsgType =
   | 'invite_generated'
   | 'identity_exported'
   | 'identity_imported'
+  | 'shares_list'
   | 'peer_status'
   | 'error'
 
@@ -109,6 +118,8 @@ export interface IpcMessage {
   error_message?: string
   invite?: string
   files?: FileEntry[]
+  shares?: ShareEntry[]
+  networks_filter?: string[]  // for add_share
   // peer_status
   conn_state?: PeerConnState
   candidate_type?: CandidateType