Add background PDF generation for published document versions

Move PDF generation from synchronous publish flow to a background polling
job. Published versions with file_id IS NULL are picked up by the job,
which generates the PDF, uploads to S3, and links the file. Export PDF
now serves stored files for published versions (with optional signature
page and watermark) and generates on the fly for drafts.

Signed-off-by: Sacha Al Himdani <sacha@getprobo.com>

pkg/docgen/generator.go

@@ -44,6 +44,9 @@ var (
 	//go:embed transfer_impact_assessments_template.html
 	transferImpactAssessmentsTemplateContent string
 
+	//go:embed signature_page_template.html
+	signaturePageTemplateContent string
+
 	templateFuncs = template.FuncMap{
 		"now":                  func() time.Time { return time.Now() },
 		"eq":                   func(a, b any) bool { return a == b },
@@ -183,6 +186,8 @@ var (
 	dataProtectionImpactAssessmentsTemplate = template.Must(template.New("dataProtectionImpactAssessments").Funcs(templateFuncs).Parse(dataProtectionImpactAssessmentsTemplateContent))
 
 	transferImpactAssessmentsTemplate = template.Must(template.New("transferImpactAssessments").Funcs(templateFuncs).Parse(transferImpactAssessmentsTemplateContent))
+
+	signaturePageTemplate = template.Must(template.New("signaturePage").Funcs(templateFuncs).Parse(signaturePageTemplateContent))
 )
 
 type (
@@ -210,6 +215,11 @@ type (
 		RequestedAt time.Time
 	}
 
+	SignaturePageData struct {
+		Signatures []SignatureData
+		Landscape  bool
+	}
+
 	ProcessingActivityTableData struct {
 		CompanyName                 string
 		CompanyHorizontalLogoBase64 string
@@ -399,6 +409,15 @@ func RenderHTML(data DocumentData) ([]byte, error) {
 	return buf.Bytes(), nil
 }
 
+func RenderSignaturePageHTML(data SignaturePageData) ([]byte, error) {
+	var buf bytes.Buffer
+	if err := signaturePageTemplate.Execute(&buf, data); err != nil {
+		return nil, fmt.Errorf("cannot execute signature page template: %w", err)
+	}
+
+	return buf.Bytes(), nil
+}
+
 func RenderProcessingActivitiesTableHTML(data ProcessingActivityTableData) ([]byte, error) {
 	var buf bytes.Buffer
 	if err := processingActivitiesTemplate.Execute(&buf, data); err != nil {