Phase 4a sub-commit 2: AppImage recipe (build-appimage.sh + make appimage)

packaging/linux/build-appimage.sh produces a single-file Linux
AppImage from a built host + Symfony tree + FrankenPHP binary.
Auto-downloads (cached in tools/, gitignored) the three pieces of
upstream tooling:

  - linuxdeploy + linuxdeploy-plugin-qt — gathers Qt runtime and QML
    modules into the AppDir, and bundles the offscreen platform
    plugin via EXTRA_PLATFORM_PLUGINS so headless CI can smoke it.
  - appimagetool — squashes the AppDir into the .AppImage.
  - runtime-x86_64 — appimagetool's prepended runtime stub, fetched
    once and passed via --runtime-file (ad-hoc downloads stalled on
    some networks).

The two stages are kept separate (linuxdeploy stages, then we invoke
appimagetool ourselves) so failures are observable rather than
swallowed by linuxdeploy's bundled-tool path.

AppDir layout matches BackendConnection's resolve* fallbacks:
  AppDir/usr/bin/<app>
  AppDir/usr/bin/frankenphp
  AppDir/usr/share/<app>/symfony/
  AppDir/usr/share/<app>/Caddyfile

examples/todo gets `make appimage`: stages a no-dev composer install
into build/staging-symfony, points the path repo at the bundle's
absolute path so Composer can find php-qml/bridge from the staging
dir, then drives build-appimage.sh. Output:
build/Todo-x86_64.AppImage (~104 MB).

Verified locally: `make appimage` produces a working AppImage; mount
+ inspect + extract all clean. Headless run requires the bundled
offscreen plugin (now wired); a real desktop launches it normally.

Includes a 64×64 placeholder PNG icon (todo.png) and a minimal
.desktop file for the example.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

examples/todo/Makefile

@@ -40,6 +40,33 @@ clean: ## Remove build artefacts
 integration: ## Run the bridge-integration test (FrankenPHP boot + HTTP/SSE round-trip + crash-recover)
 	./tests/integration.sh
 
+.PHONY: appimage
+appimage: build ## Package as a single-file Linux AppImage at build/Todo-x86_64.AppImage
+	# Composer install --no-dev in a staging copy of symfony so the
+	# dev tree (with maker-bundle etc.) is left untouched.
+	rm -rf build/staging-symfony
+	rsync -a --delete \
+		--exclude='vendor/' \
+		--exclude='var/cache/' --exclude='var/log/' \
+		$(SYMFONY_DIR)/ build/staging-symfony/
+	# Rewrite the path repo to absolute so composer can find the bundle
+	# from the staging dir (different relative depth than the source tree).
+	BUNDLE_ABS="$$(cd $(SYMFONY_DIR)/../../../framework/php && pwd)"; \
+	    sed -i "s|\"../../../framework/php\"|\"$$BUNDLE_ABS\"|" build/staging-symfony/composer.json
+	rm -f build/staging-symfony/composer.lock
+	cd build/staging-symfony && composer install --no-dev --no-interaction --classmap-authoritative
+	../../packaging/linux/build-appimage.sh \
+		--app-name todo \
+		--host-binary $(QT_BIN) \
+		--symfony-dir build/staging-symfony \
+		--frankenphp $${FRANKENPHP:-frankenphp} \
+		--caddyfile Caddyfile \
+		--desktop packaging/todo.desktop \
+		--icon packaging/todo.png \
+		--output build/Todo-x86_64.AppImage
+	@echo
+	@echo "AppImage built. Test with: ./build/Todo-x86_64.AppImage"
+
 .PHONY: quality
 quality: build ## Run PHPStan, php-cs-fixer (check), PHPUnit, qmllint, integration
 	cd ../../framework/php && composer quality

examples/todo/packaging/todo.desktop

@@ -0,0 +1,8 @@
+[Desktop Entry]
+Type=Application
+Name=php-qml Todo
+Comment=php-qml POC todo app
+Exec=todo
+Icon=todo
+Categories=Utility;
+Terminal=false