Add peer-to-peer file transfer in browser mode

Implements both pull (browse & download from a shared folder) and push
(send a file directly to a peer) using the yaw2 file protocol over WebRTC
DataChannels.

- PeerConn: handle browse/files/get/file-offer/file-accept/file-done
  control messages; stream files in 64KB chunks over f:xid binary
  DataChannels; auto-accept incoming offers (push and pull)
- PeerConn.sendFilePush(): initiate an outbound file transfer without
  requiring the peer to browse first
- BrowserAdapter: sharedFiles map, setSharedFiles(), requestBrowse(),
  requestGet(), sendFileTo() — propagates share map to all active peers
- Store: activeFilePeer, setActiveFilePeer, setSharedFiles, browseFiles,
  sendFileTo; file_complete handler triggers browser download automatically
- FileBrowser component: third-column panel listing a peer's shared files
  with name, size, and a download button
- FolderPicker component: webkitdirectory input in the sidebar (browser
  mode only) for selecting a local folder to share
- Sidebar: 📎 send-file button on peer rows (hover) with inline file picker
- App.tsx: use browser mode when WASTE_CONFIG.signalURL is set, even on
  localhost — allows testing browser mode via npm run dev with config.js
- deploy-daemon.sh: kill existing daemon before scp to avoid upload failure
  when the binary is locked; remove duplicate kill block in restart step

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

web/src/App.tsx

@@ -4,19 +4,20 @@ import { Onboarding } from './pages/Onboarding'
 import { Chat } from './pages/Chat'
 import './App.css'
 
-// When served from the anchor (non-localhost), default to browser mode.
-// When running locally, try the daemon first.
 const isLocal = window.location.hostname === 'localhost' || window.location.hostname === '127.0.0.1'
 const DAEMON_WS = import.meta.env.VITE_DAEMON_WS ?? 'ws://127.0.0.1:17338'
+const cfg = (window as unknown as { WASTE_CONFIG?: { signalURL?: string } }).WASTE_CONFIG
+// Use browser mode if a signal URL is configured, even on localhost
+const useBrowser = !isLocal || !!cfg?.signalURL
 
 export default function App() {
   const { connect, connectBrowser, daemonStatus, localPeer } = useWaste()
 
   useEffect(() => {
-    if (isLocal) {
-      connect(DAEMON_WS)
-    } else {
+    if (useBrowser) {
       connectBrowser()
+    } else {
+      connect(DAEMON_WS)
     }
   }, [connect, connectBrowser])