docs: plan backend foundation phase

docs/planning/ARCHITECTURE.md

@@ -58,6 +58,9 @@ Implementation should follow the engineering rules in
 SOLID responsibility boundaries, KISS implementation choices, and YAGNI for
 future-only abstractions.
 
+Initial typed workflow contracts are defined in
+`docs/planning/WORKFLOW_CONTRACTS.md`.
+
 Initial workflow set:
 
 - `diagnose_job_seeker`
@@ -91,6 +94,9 @@ Core progression surfaces:
 - strong-answer portfolio
 - interview-date campaign plan
 
+The first progression track is the backend developer interview seed list in
+`docs/planning/INTERVIEW_TRACKS.md`.
+
 Progression decisions should read from learner memory and grading evidence.
 They should be exposed as workflow outputs so the service can explain why a
 question, reward, or unlock appeared.