feat: add application versioning support to backend and UI

- Introduce APP_VERSION build argument and environment variable in Dockerfile.
- Load AppVersion from environment variables in the configuration loader.
- Pass the application version to the HTML renderer and expose it to templates via PageData.
- Update tests to verify the version is correctly rendered in the footer.

backend/libs/handlers/accounts_test.go

@@ -569,6 +569,9 @@ func TestHomeReflectsUploadPolicySettings(t *testing.T) {
 	if !strings.Contains(body, "Max file size: 123 MB") || !strings.Contains(body, "456 MB") {
 		t.Fatalf("home did not reflect policy settings: %s", body)
 	}
+	if !strings.Contains(body, "warpbox.dev · test ·") {
+		t.Fatalf("home footer did not include app version: %s", body)
+	}
 }
 
 func TestAPIDocsHeaderReflectsLoggedInUser(t *testing.T) {

backend/libs/handlers/upload_stage3_test.go

@@ -179,6 +179,7 @@ func newTestApp(t *testing.T) (*App, func()) {
 	logger := slog.New(slog.NewTextHandler(io.Discard, nil))
 	cfg := config.Config{
 		AppName:       "warpbox.dev",
+		AppVersion:    "test",
 		BaseURL:       "http://example.test",
 		DataDir:       filepath.Join(root, "data"),
 		StaticDir:     staticDir,
@@ -197,7 +198,7 @@ func newTestApp(t *testing.T) (*App, func()) {
 	if err != nil {
 		t.Fatalf("NewUploadService returned error: %v", err)
 	}
-	renderer, err := web.NewRenderer(cfg.TemplateDir, cfg.AppName, cfg.BaseURL)
+	renderer, err := web.NewRenderer(cfg.TemplateDir, cfg.AppName, cfg.AppVersion, cfg.BaseURL)
 	if err != nil {
 		service.Close()
 		t.Fatalf("NewRenderer returned error: %v", err)