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>

go.mod

@@ -6,14 +6,16 @@ require (
 	filippo.io/edwards25519 v1.2.0
 	github.com/google/uuid v1.6.0
 	github.com/pion/webrtc/v3 v3.3.6
-	golang.org/x/crypto v0.24.0
+	golang.org/x/crypto v0.33.0
 	modernc.org/sqlite v1.53.0
 	nhooyr.io/websocket v1.8.17
 )
 
 require (
+	git.sr.ht/~jackmordaunt/go-toast/v2 v2.0.3 // indirect
 	github.com/atotto/clipboard v0.1.4 // indirect
 	github.com/aymanbagabas/go-osc52/v2 v2.0.1 // indirect
+	github.com/bep/debounce v1.2.1 // indirect
 	github.com/charmbracelet/bubbles v1.0.0 // indirect
 	github.com/charmbracelet/bubbletea v1.3.10 // indirect
 	github.com/charmbracelet/colorprofile v0.4.1 // indirect
@@ -27,7 +29,26 @@ require (
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/dustin/go-humanize v1.0.1 // indirect
 	github.com/erikgeiser/coninput v0.0.0-20211004153227-1c3628e74d0f // indirect
+	github.com/getlantern/context v0.0.0-20190109183933-c447772a6520 // indirect
+	github.com/getlantern/errors v0.0.0-20190325191628-abdb3e3e36f7 // indirect
+	github.com/getlantern/golog v0.0.0-20190830074920-4ef2e798c2d7 // indirect
+	github.com/getlantern/hex v0.0.0-20190417191902-c6586a6fe0b7 // indirect
+	github.com/getlantern/hidden v0.0.0-20190325191715-f02dbb02be55 // indirect
+	github.com/getlantern/ops v0.0.0-20190325191751-d70cb0d6f85f // indirect
+	github.com/getlantern/systray v1.2.2 // indirect
+	github.com/go-ole/go-ole v1.3.0 // indirect
+	github.com/go-stack/stack v1.8.0 // indirect
+	github.com/godbus/dbus/v5 v5.1.0 // indirect
+	github.com/gorilla/websocket v1.5.3 // indirect
+	github.com/jchv/go-winloader v0.0.0-20210711035445-715c2860da7e // indirect
+	github.com/labstack/echo/v4 v4.13.3 // indirect
+	github.com/labstack/gommon v0.4.2 // indirect
+	github.com/leaanthony/go-ansi-parser v1.6.1 // indirect
+	github.com/leaanthony/gosod v1.0.4 // indirect
+	github.com/leaanthony/slicer v1.6.0 // indirect
+	github.com/leaanthony/u v1.1.1 // indirect
 	github.com/lucasb-eyer/go-colorful v1.3.0 // indirect
+	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mattn/go-localereader v0.0.1 // indirect
 	github.com/mattn/go-runewidth v0.0.19 // indirect
@@ -35,6 +56,7 @@ require (
 	github.com/muesli/cancelreader v0.2.2 // indirect
 	github.com/muesli/termenv v0.16.0 // indirect
 	github.com/ncruces/go-strftime v1.0.0 // indirect
+	github.com/oxtoacart/bpool v0.0.0-20190530202638-03653db5a59c // indirect
 	github.com/pion/datachannel v1.5.8 // indirect
 	github.com/pion/dtls/v2 v2.2.12 // indirect
 	github.com/pion/ice/v2 v2.3.38 // indirect
@@ -50,15 +72,24 @@ require (
 	github.com/pion/stun v0.6.1 // indirect
 	github.com/pion/transport/v2 v2.2.10 // indirect
 	github.com/pion/turn/v2 v2.1.6 // indirect
+	github.com/pkg/browser v0.0.0-20240102092130-5ac0b6a4141c // indirect
+	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/remyoudompheng/bigfft v0.0.0-20230129092748-24d4a6f8daec // indirect
 	github.com/rivo/uniseg v0.4.7 // indirect
-	github.com/stretchr/testify v1.9.0 // indirect
+	github.com/samber/lo v1.49.1 // indirect
+	github.com/stretchr/testify v1.10.0 // indirect
+	github.com/tkrajina/go-reflector v0.5.8 // indirect
+	github.com/valyala/bytebufferpool v1.0.0 // indirect
+	github.com/valyala/fasttemplate v1.2.2 // indirect
+	github.com/wailsapp/go-webview2 v1.0.22 // indirect
+	github.com/wailsapp/mimetype v1.4.1 // indirect
+	github.com/wailsapp/wails/v2 v2.12.0 // indirect
 	github.com/wlynxg/anet v0.0.3 // indirect
 	github.com/xo/terminfo v0.0.0-20220910002029-abceb7e1c41e // indirect
-	golang.org/x/net v0.22.0 // indirect
+	golang.org/x/net v0.35.0 // indirect
 	golang.org/x/sys v0.44.0 // indirect
-	golang.org/x/text v0.16.0 // indirect
+	golang.org/x/text v0.22.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 	modernc.org/libc v1.73.4 // indirect
 	modernc.org/mathutil v1.7.1 // indirect