docs(epic-3): add story context XML files for all stories

Story Context Generation Complete:
- 3-1: PDF Generation API Route context (8 ACs, Puppeteer interfaces)
- 3-2: PDF Download Composable context (8 ACs, blob handling)
- 3-3: Download Button Integration context (8 ACs, UButton binding)

Each context includes:
- Acceptance criteria mapping
- Relevant code artifacts and snippets
- Interface definitions
- Constraints and dependencies
- Test ideas per AC

Status Updates:
- All 3 stories: drafted → ready-for-dev

Files Created:
- docs/sprint-artifacts/3-1-create-pdf-generation-api-route.context.xml
- docs/sprint-artifacts/3-2-create-pdf-download-composable.context.xml
- docs/sprint-artifacts/3-3-connect-download-button-to-pdf-generation.context.xml

Files Modified:
- docs/sprint-artifacts/sprint-status.yaml
- docs/sprint-artifacts/3-1-create-pdf-generation-api-route.md
- docs/sprint-artifacts/3-2-create-pdf-download-composable.md
- docs/sprint-artifacts/3-3-connect-download-button-to-pdf-generation.md

Ready for: Dev Agent implementation

docs/sprint-artifacts/3-2-create-pdf-download-composable.md

@@ -1,6 +1,6 @@
 # Story 3.2: Create PDF Download Composable
 
-Status: drafted
+Status: ready-for-dev
 
 ## Story