feat: add learner memory ingestion

.planning/phases/003-learner-memory/003-SUMMARY.md

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+# Phase 3 Summary
+
+**Status:** Complete
+**Completed:** 2026-04-26
+
+## Delivered
+
+- Added `internal/learnermemory` for profile, concept mastery,
+  misconceptions, interventions, review schedule, and snapshots.
+- Added in-memory learner memory store and service.
+- Extended `GradedAnswer` with `user_id`.
+- Implemented `ExtractLearningMemory` in the workflow stub.
+- Wired diagnostic answer submission to memory extraction and evidence-backed
+  memory application.
+- Added `GET /api/v1/learners/{userID}/memory`.
+- Added unit and HTTP tests for memory application and readback.
+
+## Verification
+
+```powershell
+gofmt -w cmd internal
+go test ./...
+openspec validate bootstrap-job-tutor-platform --strict
+```
+
+Additional smoke check:
+
+- Diagnostic create/answer followed by learner memory read returned 1 mastery
+  entry for `user-1`.
+
+## Deferred
+
+- Durable database persistence.
+- Memory decay and ranking.
+- Repeated-mistake clustering beyond the current evidenced candidate writes.
+- Progression readiness map UI/API.