feat: add progression readiness api

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

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+# Phase 4 Verification
+
+## Verdict
+
+PASS
+
+## Requirement Coverage
+
+- PROG-01: PASS. Readiness map API returns learner concept readiness.
+- PROG-02: PASS. Each concept maps to a challenge ladder level.
+- PROG-03: PASS. Next challenge selection targets the weakest evidenced
+  learner-memory concept.
+- PROG-04: PASS. Boss unlocks are produced only from stable evidenced concepts.
+- PROG-05: PASS. Rewards are deterministic, evidence-backed, and do not punish
+  missed days or use random reward mechanics.
+
+## Evidence
+
+- `go test ./...` passed.
+- `openspec validate bootstrap-job-tutor-platform --strict` passed.
+- Live diagnostic create/answer plus readiness and next-challenge smoke passed.
+- Go source line-count check passed.
+
+## Residual Risk
+
+Progression is currently an in-memory projection. It is enough for MVP proof but
+will need persisted campaign state before real streaks or long-running
+readiness histories.