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.css

@@ -81,9 +81,30 @@ details summary { color: var(--muted); font-size: 12px; cursor: pointer; }
 .message { display: flex; align-items: baseline; gap: 0; padding: 2px 16px; line-height: 1.5; }
 .message:hover { background: rgba(255,255,255,0.02); }
 .message-ts { color: var(--muted); font-size: 11px; white-space: nowrap; flex-shrink: 0; width: 52px; }
-.message-alias { font-weight: 600; font-size: 13px; text-align: right; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; flex-shrink: 0; width: 90px; padding-right: 10px; }
+.message-alias { font-weight: 600; font-size: 13px; text-align: left; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; flex-shrink: 0; width: 90px; padding-right: 10px; }
 .message.mine .message-alias { color: var(--accent); }
 .message-text { word-break: break-word; font-size: 14px; color: var(--text); }
 .compose { display: flex; gap: 8px; padding: 10px 16px; border-top: 1px solid var(--border); }
 .compose input { flex: 1; width: auto; }
 .compose button { flex-shrink: 0; }
+
+/* ── file browser panel ── */
+.chat-layout.has-file-browser { grid-template-columns: var(--sidebar-w) 1fr 280px; }
+.file-browser { display: flex; flex-direction: column; background: var(--surface); border-left: 1px solid var(--border); }
+.file-browser-header { display: flex; align-items: center; justify-content: space-between; padding: 10px 12px; border-bottom: 1px solid var(--border); }
+.file-browser-title { font-size: 13px; font-weight: 600; }
+.file-browser-close { background: none; color: var(--muted); font-size: 14px; padding: 2px 6px; }
+.file-browser-close:hover { color: var(--text); background: none; }
+.file-browser-empty { padding: 16px 12px; color: var(--muted); font-size: 13px; }
+.file-list { list-style: none; padding: 4px 0; overflow-y: auto; flex: 1; }
+.file-entry { display: flex; align-items: center; gap: 6px; padding: 5px 12px; }
+.file-entry:hover { background: rgba(255,255,255,0.04); }
+.file-entry-name { flex: 1; font-size: 13px; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.file-entry-size { color: var(--muted); font-size: 11px; flex-shrink: 0; }
+.file-entry-dl { background: none; color: var(--accent); font-size: 14px; padding: 1px 4px; flex-shrink: 0; }
+.file-entry-dl:hover { background: rgba(124,106,247,0.15); }
+
+/* ── folder picker ── */
+.folder-picker { width: 100%; }
+.folder-picker-btn { background: var(--surface); color: var(--muted); border: 1px solid var(--border); font-size: 12px; padding: 5px 10px; border-radius: 4px; width: 100%; text-align: left; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
+.folder-picker-btn:hover { color: var(--text); border-color: var(--accent); background: var(--surface); }