feat: add progression readiness api

.planning/phases/004-progression/004-SUMMARY.md

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+# Phase 4 Summary
+
+**Status:** Complete
+**Completed:** 2026-04-26
+
+## Delivered
+
+- Added `internal/progression` for readiness projection and next challenge
+  selection.
+- Added role readiness map calculation from learner memory evidence.
+- Added deterministic challenge ladder mapping.
+- Added evidence-backed rewards and boss-question unlocks.
+- Added HTTP endpoints:
+  - `GET /api/v1/learners/{userID}/readiness-map`
+  - `GET /api/v1/learners/{userID}/next-challenge`
+- Added progression unit tests and HTTP flow coverage.
+
+## Verification
+
+```powershell
+gofmt -w cmd internal
+go test ./...
+openspec validate bootstrap-job-tutor-platform --strict
+```
+
+Additional smoke check:
+
+- Diagnostic create/answer followed by readiness-map and next-challenge reads
+  returned readiness `75`, one concept, and a typed challenge.
+
+## Deferred
+
+- Frontend readiness visualization.
+- Persistent campaign and streak state.
+- Multi-concept cluster graph beyond simple stable-count boss unlock.