docs(D.2b): container-switching handoff + flag stale M1.5 banner

Banks the next clean inventory win (container-switching: Use 0x0036 -> ViewContents
0x0196 full-replace + the selected-container indicator that retires AP-56) as a
handoff for a fresh session, per the late-session-handoff lesson. Wire layer
already exists; design sketch + open questions captured.

Also flags the CLAUDE.md "Current state" banner as stale — it still tracks M1.5
(indoor world, 2026-06-14) while the active stream has been the D.2b retail-UI
track for weeks. Left the milestone reframing for a fresh reconciliation against
the milestones doc rather than a tired guess.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -121,6 +121,13 @@ M2 (CombatMath) deferred. Detail in ISSUES (#135–#138) + the render/physics di
 Recent closes (2026-06-14): #135, #136. Keep this paragraph ≤6 lines + pointers — detail
 in the docs below, NOT here.
 
+**⚠ Reconcile (banner stale as of 2026-06-22):** the active recent work stream has been the
+parallel **D.2b retail-UI track** (inventory window / panels — the inventory empty-slot art
+shipped + was visually confirmed this session; next is container-switching), NOT the M1.5
+dungeon items above. See [`claude-memory/project_d2b_retail_ui.md`] + the handoff
+`docs/research/2026-06-22-container-switching-handoff.md`. Decide in the milestones doc whether
+M1.5 is paused or D.2b retail-UI is its own milestone, then rewrite this banner.
+
 For canonical state, read in this order:
 - [`docs/plans/2026-05-12-milestones.md`](docs/plans/2026-05-12-milestones.md) — milestone targets + freeze list per milestone
 - [`docs/plans/2026-04-11-roadmap.md`](docs/plans/2026-04-11-roadmap.md) — what's shipped, what's in flight, what's next