feat: download dirs, file transfer resume, Wails desktop app, PWA, CI

Daemon:
- Per-network download directories (-download-dir flag, set_download_dir IPC)
- File transfer resume after disconnection: .tmp.meta sidecars survive
  interruption; resume_offset in file-accept lets sender seek and continue
- set_download_dir IPC command; download_dir reported in state_snapshot

Protocol:
- PeerMessage.ResumeOffset (EXT-006) for file transfer resume
- IpcMessage.ShareNetworks json tag changed from "networks" to "network_ids"
  to fix duplicate json tag collision with Networks []NetworkInfo

Desktop app (cmd/app):
- Wails v2 shell embedding daemon logic directly (no subprocess)
- System tray on Linux/Windows via getlantern/systray; macOS hides to Dock
- OS notifications for message_received and file_complete via Wails events
- notray build tag for headless/CI builds without GTK tray headers
- build-app.sh: builds web frontend, copies dist, runs wails build

Web / PWA:
- manifest.json + Apple touch icon meta tags for mobile "Add to Home Screen"
- PNG icons (192px, 512px, 180px) generated from SVG
- Wails EventsOn("notify") hook in App.tsx for native OS notifications

CI:
- .gitea/workflows/build.yml: server binaries cross-compiled for 5 platforms,
  desktop app for Linux amd64, release artifacts published on v* tags

Docs:
- README: download dir, file transfer resume, desktop app, PWA, CI sections
- EXTENSIONS.md: EXT-004 daemon mode marked shipped; EXT-006 resume added
- FUTURE.md: roadmap updated

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

web/src/App.tsx

@@ -10,6 +10,35 @@ const cfg = (window as unknown as { WASTE_CONFIG?: { signalURL?: string } }).WAS
 // Use browser mode if a signal URL is configured, even on localhost
 const useBrowser = !isLocal || !!cfg?.signalURL
 
+// Wails runtime is injected at /wails/runtime.js when running inside the desktop app.
+// EventsOn/EventsOff are no-ops in plain browser mode.
+type WailsRuntime = { EventsOn: (event: string, cb: (data: unknown) => void) => void }
+const wails = (window as unknown as { runtime?: WailsRuntime }).runtime
+
+function useWailsNotifications() {
+  useEffect(() => {
+    if (!wails) return
+
+    const handler = (data: unknown) => {
+      const { title, body } = data as { title: string; body: string }
+      if (Notification.permission === 'granted') {
+        new Notification(title, { body })
+      } else if (Notification.permission !== 'denied') {
+        Notification.requestPermission().then(p => {
+          if (p === 'granted') new Notification(title, { body })
+        })
+      }
+    }
+
+    wails.EventsOn('notify', handler)
+    return () => {
+      // EventsOff added in Wails v2.4; guard in case of older runtime.
+      ;(window as unknown as { runtime?: { EventsOff?: (...e: string[]) => void } })
+        .runtime?.EventsOff?.('notify')
+    }
+  }, [])
+}
+
 export default function App() {
   const { connect, connectBrowser, daemonStatus, localPeer } = useWaste()
 
@@ -21,6 +50,8 @@ export default function App() {
     }
   }, [connect, connectBrowser])
 
+  useWailsNotifications()
+
   if (daemonStatus !== 'connected' || !localPeer) {
     return <Onboarding status={daemonStatus} />
   }