feat: add ontology material ingestion

.planning/phases/005-ontology-materials/005-CONTEXT.md

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+# Phase 5 Context: Ontology and Learning Materials
+
+**Status:** Ready for execution
+**Started:** 2026-04-26
+
+## Goal
+
+Accept learning material input and produce source-backed ontology candidates.
+
+## Inputs
+
+- OpenSpec `learning-ontology` requirements.
+- Existing workflow contracts for `OntologyGap`.
+- Backend Developer Interview seed concepts.
+
+## Decisions
+
+- Use an in-memory ontology store for MVP proof.
+- Accept JSON material ingestion before multipart file upload.
+- Mark all generated nodes, edges, and gaps as `candidate`.
+- Preserve source evidence for every supported ontology candidate.
+
+## Boundaries
+
+In scope:
+
+- Material ingestion API.
+- Source-backed ontology candidate nodes and edges.
+- Gap detection for missing prerequisites and weak evidence.
+- Ontology snapshot API.
+
+Out of scope:
+
+- File storage.
+- PDF/PPT parsing.
+- Human review UI.
+- Canonical promotion workflow.