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>

cmd/app/tray.go

@@ -0,0 +1,35 @@
+//go:build !darwin && !notray
+
+package main
+
+import (
+	_ "embed"
+
+	"github.com/getlantern/systray"
+	"github.com/wailsapp/wails/v2/pkg/runtime"
+)
+
+//go:embed appicon.png
+var trayIcon []byte
+
+func (a *App) startTray() {
+	go systray.Run(func() {
+		systray.SetIcon(trayIcon)
+		systray.SetTooltip("waste")
+
+		mShow := systray.AddMenuItem("Open waste", "Show the waste window")
+		systray.AddSeparator()
+		mQuit := systray.AddMenuItem("Quit", "Quit waste")
+
+		for {
+			select {
+			case <-mShow.ClickedCh:
+				runtime.WindowShow(a.ctx)
+			case <-mQuit.ClickedCh:
+				systray.Quit()
+				runtime.Quit(a.ctx)
+				return
+			}
+		}
+	}, func() {})
+}