gui: add Wails v3 desktop app skeleton

- Go upgraded to 1.25.10 (required by Wails v3)
- Wails v3 installed (alpha.96)
- Frontend: Svelte+Vite scaffold in frontend/
- guimain.go: Wails GUI entry point (compiled with -tags gui)
- wails_service.go: stub service for Wails bindings
- Verstak desktop binary builds: go build -tags gui -o verstak-gui .
- CLI (./cmd/verstak/) unaffected
- Legacy HTTP GUI (internal/gui/) preserved as prototype
- Build: 24MB ELF binary with GTK4/WebKit2GTK-6

Build commands:
  CLI:  go build -o verstak ./cmd/verstak/
  GUI:  cd frontend && npm run build && go build -tags gui -o verstak-gui .

build/linux/appimage/build.sh

@@ -0,0 +1,35 @@
+#!/usr/bin/env bash
+# Copyright (c) 2018-Present Lea Anthony
+# SPDX-License-Identifier: MIT
+
+# Fail script on any error
+set -euxo pipefail
+
+# Define variables
+APP_DIR="${APP_NAME}.AppDir"
+
+# Create AppDir structure
+mkdir -p "${APP_DIR}/usr/bin"
+cp -r "${APP_BINARY}" "${APP_DIR}/usr/bin/"
+cp "${ICON_PATH}" "${APP_DIR}/"
+cp "${DESKTOP_FILE}" "${APP_DIR}/"
+
+if [[ $(uname -m) == *x86_64* ]]; then
+    # Download linuxdeploy and make it executable
+    wget -q -4 -N https://github.com/linuxdeploy/linuxdeploy/releases/download/continuous/linuxdeploy-x86_64.AppImage
+    chmod +x linuxdeploy-x86_64.AppImage
+
+    # Run linuxdeploy to bundle the application
+    ./linuxdeploy-x86_64.AppImage --appdir "${APP_DIR}" --output appimage
+else
+    # Download linuxdeploy and make it executable (arm64)
+    wget -q -4 -N https://github.com/linuxdeploy/linuxdeploy/releases/download/continuous/linuxdeploy-aarch64.AppImage
+    chmod +x linuxdeploy-aarch64.AppImage
+
+    # Run linuxdeploy to bundle the application (arm64)
+    ./linuxdeploy-aarch64.AppImage --appdir "${APP_DIR}" --output appimage
+fi
+
+# Rename the generated AppImage
+mv "${APP_NAME}*.AppImage" "${APP_NAME}.AppImage"
+