expose project graph data and harden builder resolution

[matthewpeterkort]

Loom Explorer Builder stack

Layer 3 of 6. Merge strictly in order: #17 → #18 → #19 → #20 → #21 → #22.

Previous: #18
Next: #20

What changed

• exposes the populated project graph through the GraphQL builder surface
• resolves project-scoped data identity correctly
• normalizes FHIR resource row grains
• tolerates conditional discovered schemas

Why

The lifecycle layer needs reliable project-specific graph discovery before a frontend can build valid recipes from loaded data.

Impact

Builder clients receive usable project graph metadata and stable schema and grain behavior.

Validation

The complete stack tip (b281499c) passes go test ./.... This layer also runs independent GitHub CI, generated-code checks, and a server image build.

[matthewpeterkort]

Archiving this superseded stack layer. Current stable baseline is PR #17 at 6c49754. The branch is preserved for historical reference; future Explorer work should be rebased or selectively ported onto current #17.