fix(adapter): resolve all WHYNOT-WP-0002 drift — designbook-refresh green

Triage the three surfaced divergences the governance-correct way (no stack->React
back-edit, no ir/ hand-edit); make adapt-lit/parity-lit/designbook-refresh now
exit 0:

- PipelineStrip: documented TAG_OVERRIDES in scripts/ir-extract.mjs maps the
  React 'PipelineStrip' to the established tag wn-pipeline (the web-component tag
  is an IR-projection detail, not React-dictated; the component name stays
  faithful). Tag now matches the element; parity tests it (no longer skipped).
- PageHeader.actions: the drift detector now collects each element's named slots
  and treats an IR prop honoured by a same-named slot (<slot name="actions">) as
  satisfied (prop-via-slot, informational) rather than prop-missing.
- Sidebar.current: recorded as an auditable accepted divergence in
  adapters/lit/drift.accepted.json (React monolithic 'current' key vs Lit per-item
  'active' on composable <wn-sidebar-item>) — listed, downgraded to info, not gated.

Rendered surfaces (src/, examples/) untouched — verified zero diff; parity renders
all 10 components green. Adapt/parity outputs idempotent (stable re-run).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

adapters/lit/drift.accepted.json

@@ -0,0 +1,17 @@
+{
+  "_comment": "Human-curated accepted divergences — the auditable output of drift triage (WHYNOT-WP-0002). An entry downgrades a specific drift issue to an informational, justified note so it does not gate make adapt-lit/parity-lit. Use ONLY for intentional React<->Lit modelling differences, never to silence a real defect. Keyed by component + drift kind + prop. See .claude/rules/designbook-propagation.md.",
+  "accepted": [
+    {
+      "component": "Sidebar",
+      "kind": "prop-missing",
+      "prop": "current",
+      "rationale": "Composition divergence (intentional). The React Sidebar is monolithic and takes a `current` selection-key prop, comparing it against its own internal NAV_ITEMS. The Lit stack decomposes the sidebar into <wn-sidebar> + <wn-sidebar-group> + <wn-sidebar-item>, modelling selection as per-item `active` state on the slotted children rather than a container-level key. There is no single `current` attribute to honour on <wn-sidebar>; the contract is satisfied compositionally. Reconcile upstream only if the React designbook is ever made composable."
+    },
+    {
+      "component": "Sidebar",
+      "kind": "variant-axis-missing",
+      "prop": "current",
+      "rationale": "Same composition divergence as Sidebar.current above — the `current` variant axis is expressed as item-level `active` on <wn-sidebar-item>, not as a <wn-sidebar> property."
+    }
+  ]
+}