Desktop client (warp-desktop) with Wails v3

apps/desktop is the web client in a native window. It embeds the same
build warp-web does and serves it through the same Go package, so every
screen is shared. Unlike warp-web it proxies nothing: the client calls the
homeserver directly, and the CSP allows the homeserver plus any https:
and wss: origin for the call backend.

- First run asks for the homeserver: a server name or address, with
  .well-known discovery and a /versions check; File > Change homeserver
  asks again. Signed-in sessions keep their own base URL, so a change
  never sends one server's token to another.
- Links to other sites open in the system browser (/_desktop/links.js,
  added to index.html); only http, https and mailto are opened.
- One instance at a time, since sessions and keys live in the webview's
  storage.
- Dev builds open the DevTools Protocol on Windows when
  WARP_DESKTOP_REMOTE_DEBUGGING_PORT is set, for scripted testing.
- Packaging: icon, version info and manifest in the Windows exe, a macOS
  .app with camera and microphone descriptions, Linux packages via nfpm.
  Make targets: desktop, desktop-run, desktop-test, desktop-resources,
  desktop-macos, desktop-linux.

Web client: host and client move out of internal/ so the desktop app can
import them, and host gains AnyCallOrigin. The Dockerfile, .dockerignore
and the vite output path follow the move.

Pinned to Wails v3.0.0-beta.27.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

apps/desktop/cmd/warp-desktop/debug_dev.go

@@ -0,0 +1,18 @@
+//go:build !production
+
+package main
+
+import (
+	"os"
+	"strconv"
+)
+
+// devBrowserArgs opens the Chrome DevTools Protocol on Windows when
+// WARP_DESKTOP_REMOTE_DEBUGGING_PORT is set, so a script or Playwright can
+// drive the app's webview. Production builds leave it out.
+func devBrowserArgs() []string {
+	if p, err := strconv.Atoi(os.Getenv("WARP_DESKTOP_REMOTE_DEBUGGING_PORT")); err == nil && p > 0 {
+		return []string{"--remote-debugging-port=" + strconv.Itoa(p)}
+	}
+	return nil
+}