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/FolderPicker.tsx

@@ -0,0 +1,43 @@
+import { useRef, useState } from 'react'
+import { useWaste } from '../store'
+
+export function FolderPicker() {
+  const { setSharedFiles } = useWaste()
+  const inputRef = useRef<HTMLInputElement>(null)
+  const [label, setLabel] = useState<string | null>(null)
+
+  function onChange(e: React.ChangeEvent<HTMLInputElement>) {
+    const fileList = e.target.files
+    if (!fileList || fileList.length === 0) return
+    const map = new Map<string, File>()
+    for (let i = 0; i < fileList.length; i++) {
+      const f = fileList[i]
+      map.set(f.name, f)
+    }
+    setSharedFiles(map)
+    const first = fileList[0]
+    const parts = (first.webkitRelativePath || first.name).split('/')
+    setLabel(`${parts[0]} (${map.size} file${map.size !== 1 ? 's' : ''})`)
+  }
+
+  return (
+    <div className="folder-picker">
+      <input
+        ref={inputRef}
+        type="file"
+        // @ts-expect-error webkitdirectory is non-standard
+        webkitdirectory=""
+        multiple
+        style={{ display: 'none' }}
+        onChange={onChange}
+      />
+      <button
+        className="folder-picker-btn"
+        onClick={() => inputRef.current?.click()}
+        title="Share a folder with peers"
+      >
+        {label ?? '+ Share folder'}
+      </button>
+    </div>
+  )
+}