docs(phase6b): document curriculum expansion

PHASE6B_ROOT_CURRICULUM_EXPANSION.md — the phase summary: what was
authored per course, the is_required extension, the capstone unlock
fix, verified scenario coverage before/after (44 -> 88 of 98, 89.8%,
by direct query not estimate), and honest known limitations/Phase 6C
recommendations.

ROOT_CAPSTONE_READINESS.md — the readiness module and the server-side
unlock fix in full detail, including why the module's completion and
the real assessment's unlock gate are deliberately independent systems.

Updated ROOT_CURRICULUM_INVENTORY.md (Phase 6B coverage numbers),
ROOT_PROGRAM_ARCHITECTURE.md (ROOT 08/09 PARTIAL, new module lists per
course), COURSE_CONTENT_MODEL.md (is_required completion rule, a new
content-versioning section per this phase's own requirement),
COURSE_AUTHORING_STANDARD.md (classifying near-duplicate/advanced
scenarios), ENGINEERING_SOP.md (new Phase 6B section),
REMOTE_AND_SELF_PACED_ARCHITECTURE.md (cross-reference), and
platform/README.md (e2e-phase6b.js, the Phase 6B rehearsal, isolation-
per-suite regression guidance).

Co-Authored-By: Claude Sonnet 5 <[email protected]>

docs/COURSE_AUTHORING_STANDARD.md

@@ -64,6 +64,17 @@ connects what was just taught to the incident the student is about to solve, wit
 the scenario's own hints/solution — the Lab's own progressive hints stay the only place the
 actual answer path lives.
 
+### Classifying near-duplicate or advanced scenarios (Phase 6B)
+
+When two scenarios teach essentially the same concept (e.g. `pod-security-context` and
+`cks-pod-security-context`), don't wire both as required core labs — pick the better-fitting one
+as CORE and mark the other `is_required = false` as INDEPENDENT PRACTICE (see
+`docs/ROOT_CURRICULUM_COVERAGE_MATRIX.md`'s "duplicate concepts identified" for worked examples).
+Likewise, a genuinely harder or more niche scenario (CKS-exam-style, a less commonly needed
+skill) belongs as `is_required = false` GUIDED/ADVANCED practice, not force-fit into the
+required core path just because it exists — see `docs/COURSE_CONTENT_MODEL.md`'s optional-vs-
+required section for how this affects module completion.
+
 ## 9. Knowledge check
 
 A handful of self-check questions with answers shown inline (not a graded exam — that's what the