docs: record D2-W3-B landing; mark Phase D2 complete; preserve deferred panel indicator

Move D2-W3-B (item-level mode actions + W3-A polish) from PLAN.md to COMPLETED.md.
Phase D2 two-canvas sub-phase functionally complete; panel UI indicator explicitly
deferred, not dropped.

PLAN.md

@@ -119,32 +119,14 @@ landed milestone.
 > point lands, doc-keeper moves it to `COMPLETED.md`.
 >
 > **D2-W1 (pure lane extension), D2-W2 (shell: lane application + new-content
-> detection), and D2-W3-A (lane minting + item→lane assignment + persist
-> round-trip) have landed** — see `COMPLETED.md`.
-
-## D2-W3-B — two-canvas actions + panel UI indicators
-**Goal:** Any new lane/mode-management actions (bindable in the Actions list), and
-any panel UI indicator for lane/mode state. The persist slice and the
-lane-ownership index round-trip were completed in D2-W3-A; this wave closes the
-remaining UI and action surface.
-See CONTEXT.md §Two-canvas sub-phase (Module architecture — persistence).
-**Verify (in DAW):** Lane/mode-management actions are registered and bindable in
-the Actions list; the panel UI indicator reflects the current lane/mode state.
-**Depends on:** D2-W3-A.
-
-- [ ] Any new lane/mode-management actions (`command_id`/`gaccel`/`hookcommand`);
-  bindable in the Actions list.
-- [ ] Any panel UI indicator for lane/mode state.
-
-**D2-W3-A code-review polish (fold into this wave):**
-- [ ] Simplify the redundant per-mint `I_NUMFIXEDLANES` re-read in `view.cpp`
-  (`applyMintPlan`): a single grow-and-track pass removes the second
-  `GetMediaTrackInfo_Value` call inside the mint loop.
-- [ ] Optional shared item-read helper to remove duplicated `itemGuid`/`itemLaneName`
-  read logic between `view.cpp` and `bank_panel.cpp`.
-- [ ] Optional defensive note/check in `reconcileManagedLanes` for the edge case
-  where a managed lane name encodes an unregistered mode id (log and skip rather
-  than silently record an orphaned ownership entry).
+> detection), D2-W3-A (lane minting + item→lane assignment + persist round-trip),
+> and D2-W3-B (item-level mode actions + W3-A polish) have all landed** — see
+> `COMPLETED.md`. **Phase D2 is functionally complete.**
+>
+> **Deferred:** panel UI indicator for per-track lane/mode state (a per-track
+> lane-split marker). The mode switch already shows the active mode; no natural
+> cheap home for a per-track indicator was found in the bank panel. Explicitly
+> deferred — not silently dropped. Can be picked up later if wanted.
 
 ---