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/components/FileBrowser.tsx

@@ -0,0 +1,48 @@
+import { useWaste } from '../store'
+import { BrowserAdapter } from '../adapter/browser'
+
+function fmt(bytes: number): string {
+  if (bytes < 1024) return `${bytes} B`
+  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`
+  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`
+}
+
+export function FileBrowser() {
+  const { activeFilePeer, fileLists, setActiveFilePeer, adapter, connectedPeers } = useWaste()
+
+  if (!activeFilePeer) return null
+
+  const peer = connectedPeers.find(p => p.id === activeFilePeer)
+  const files = fileLists[activeFilePeer] ?? null
+
+  function download(name: string) {
+    if (adapter instanceof BrowserAdapter) {
+      adapter.requestGet(activeFilePeer!, name)
+    }
+  }
+
+  return (
+    <div className="file-browser">
+      <div className="file-browser-header">
+        <span className="file-browser-title">Files · {peer?.alias ?? activeFilePeer.slice(0, 8)}</span>
+        <button className="file-browser-close" onClick={() => setActiveFilePeer(null)}>✕</button>
+      </div>
+
+      {files === null ? (
+        <div className="file-browser-empty">Loading…</div>
+      ) : files.length === 0 ? (
+        <div className="file-browser-empty">No files shared</div>
+      ) : (
+        <ul className="file-list">
+          {files.map(f => (
+            <li key={f.name} className="file-entry">
+              <span className="file-entry-name">{f.name}</span>
+              <span className="file-entry-size">{fmt(f.size_bytes)}</span>
+              <button className="file-entry-dl" onClick={() => download(f.name)}>↓</button>
+            </li>
+          ))}
+        </ul>
+      )}
+    </div>
+  )
+}