feat: add us-cpa pdf renderer

docs/us-cpa.md

@@ -122,6 +122,22 @@ Current implemented topics:
 - standard deduction
 - Schedule C / sole proprietorship reporting trigger
 
+## Form Rendering
+
+Current rendering path:
+
+- official IRS PDFs from the cached tax-year corpus
+- overlay rendering onto those official PDFs using `reportlab` + `pypdf`
+- artifact manifest written to `output/artifacts.json`
+
+Current rendered form support:
+
+- Form 1040 overlay artifact generation
+
+Current review rule:
+
+- overlay-rendered artifacts are marked `reviewRequired: true`
+
 ## Scope Rules
 
 - U.S. federal individual returns only in v1