- Created comprehensive json-schema-reference.md with:
- Top-level structure documentation
- Document metadata, page result, span, block fields
- Table structure (row/cell) with examples
- Form fields and signatures (Phase 7 placeholders)
- Receipts and coordinate system docs
- Cross-references to plan sections (INV-11, Phase 6.1, etc.)
- Added to mdBook SUMMARY.md as top-level reference page
- All examples use real JSON from the schema
- Builds successfully (46KB HTML output)
Acceptance criteria:
- PASS: docs/user-docs/src/json-schema-reference.md exists
- PASS: Covers all top-level types and enums (Document, Page, Span, Block, Table, FormField, Signature, Receipt)
- PASS: Examples for each major type
- PASS: mdBook renders cleanly (verified)
- PASS: Cross-references to plan sections included
Closes: pdftract-5boam
