docs(13): create phase 13 AI field placement plan

4 plans in 4 sequential waves covering:
- Plan 01 (TDD): openai install, extract-text.ts, field-placement.ts, aiCoordsToPagePdfSpace unit test
- Plan 02: POST /api/documents/[id]/ai-prepare route with all guards
- Plan 03: UI wiring — aiPlacementKey in FieldPlacer, AI Auto-place button in PreparePanel
- Plan 04: Unit test gate + human E2E verification checkpoint

Satisfies AI-01, AI-02. Completes v1.1 Smart Document Preparation milestone.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.planning/ROADMAP.md

@@ -291,8 +291,8 @@ Plans:
 
 Plans:
 - [ ] 13-01-PLAN.md — lib/ai/extract-text.ts (pdfjs-dist legacy build, server-only), lib/ai/field-placement.ts (GPT-4o-mini structured output, manual JSON schema, server-only guard), aiCoordsToPagePdfSpace() utility + unit test
-- [ ] 13-02-PLAN.md — POST /api/documents/[id]/ai-prepare route (orchestrate extract + AI call + coordinate conversion + field write), "AI Auto-place" button in PreparePanel with loading state
-- [ ] 13-03-PLAN.md — AI pre-fill: map client profile fields (name, property address, date) to placed text fields; agent review step before fields are committed
+- [ ] 13-02-PLAN.md — POST /api/documents/[id]/ai-prepare route: auth + OPENAI_API_KEY guards, extract PDF text, call classifyFieldsWithAI, write fields to DB, return { fields, textFillData }
+- [ ] 13-03-PLAN.md — UI wiring: aiPlacementKey prop in FieldPlacer + PdfViewerWrapper thread-through; "AI Auto-place Fields" button (violet) in PreparePanel; DocumentPageClient handleAiAutoPlace with textFillData merge and preview reset
 - [ ] 13-04-PLAN.md — Integration test with full 20-page Utah REPC + full Phase 13 human verification checkpoint
 
 ## Progress