docs: restructure metagraph-module.md for clarity and reduced redundancy
- Eliminate 4x redundancy on SchemaBuilder removal (was in Overview, Equivalence section, DD1, DD2)
- Remove forward references to DD numbers that break reading flow
- Separate specification from rationale (DDs capture decisions, body specifies)
- Fix Type.Ref inconsistency in Edge Constraints example (should use Metagraph.Import per DD2)
- Expand 'Why TypeBox Modules' with the three friction points it solves
- Add Performance subsection, Codegen Path, Transition table, Implementation Path
- Restore Relationship to Other Packages table
- Remove historical artifacts (SchemaBuilder equivalence internals, Type.Any migration notes)
- 887 lines → 694 lines (22% reduction)
glm-5.1
6c3ed598db