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>

.gitea/workflows/build.yml

@@ -0,0 +1,120 @@
+name: Build
+
+on:
+  push:
+    tags:
+      - 'v*'
+  workflow_dispatch:
+
+jobs:
+  # ── Server binaries (no CGo, cross-compile freely) ───────────────────────────
+
+  server:
+    name: Server binaries
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        include:
+          - goos: linux
+            goarch: amd64
+          - goos: linux
+            goarch: arm64
+          - goos: darwin
+            goarch: amd64
+          - goos: darwin
+            goarch: arm64
+          - goos: windows
+            goarch: amd64
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - name: Build daemon + anchor
+        env:
+          GOOS: ${{ matrix.goos }}
+          GOARCH: ${{ matrix.goarch }}
+          CGO_ENABLED: "0"
+        run: |
+          SUFFIX="${{ matrix.goos }}-${{ matrix.goarch }}"
+          [ "${{ matrix.goos }}" = "windows" ] && EXT=".exe" || EXT=""
+          go build -trimpath -ldflags="-s -w" -o "dist/waste-daemon-${SUFFIX}${EXT}" ./cmd/daemon
+          go build -trimpath -ldflags="-s -w" -o "dist/waste-anchor-${SUFFIX}${EXT}" ./cmd/anchor
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: server-${{ matrix.goos }}-${{ matrix.goarch }}
+          path: dist/
+
+  # ── Desktop app (Wails, requires CGo + webview libs) ─────────────────────────
+  # Runs only on Linux amd64 with the default runner.
+  # For macOS/Windows desktop builds, add self-hosted runners with those platforms
+  # and duplicate this job (adjusting the runs-on and platform deps).
+
+  desktop-linux:
+    name: Desktop app (Linux amd64)
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - uses: actions/setup-go@v5
+        with:
+          go-version-file: go.mod
+
+      - uses: actions/setup-node@v4
+        with:
+          node-version: '20'
+
+      - name: Install Wails CLI
+        run: go install github.com/wailsapp/wails/v2/cmd/wails@latest
+
+      - name: Install platform dependencies
+        run: |
+          sudo apt-get update -q
+          sudo apt-get install -y \
+            libgtk-3-dev \
+            libwebkit2gtk-4.0-dev \
+            libayatana-appindicator3-dev
+
+      - name: Build frontend
+        run: |
+          cd web
+          npm ci
+          npm run build
+          cp -r dist ../cmd/app/frontend/dist
+
+      - name: Build desktop app
+        run: |
+          mkdir -p dist
+          cd cmd/app
+          wails build -trimpath -ldflags="-s -w" -o ../../dist/waste-linux-amd64
+
+      - uses: actions/upload-artifact@v4
+        with:
+          name: desktop-linux-amd64
+          path: dist/waste-linux-amd64
+
+  # ── Release: collect all artifacts and publish ────────────────────────────────
+
+  release:
+    name: Publish release
+    needs: [server, desktop-linux]
+    runs-on: ubuntu-latest
+    if: startsWith(github.ref, 'refs/tags/')
+
+    steps:
+      - uses: actions/download-artifact@v4
+        with:
+          path: artifacts/
+          merge-multiple: true
+
+      - name: Create release
+        uses: https://gitea.com/actions/gitea-release-action@main
+        with:
+          token: ${{ secrets.RELEASE_TOKEN }}
+          files: artifacts/*
+          prerelease: ${{ contains(github.ref_name, '-') }}