feat(fp): WP-10 — CIBG button fidelity

Fix button atom's dead .btn-outline-primary → .btn-secondary; add 'ghost'
variant (.btn-ghost, CIBG-documented). RTE toolbar drops invented
.btn-outline-secondary/.btn-sm for .btn-ghost. file-input already used the
correct vendored .btn-upload pattern from the earlier CIBG UI fidelity
pass — no change needed there (documented as a deviation).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

docs/backlog/WP-10-button-fidelity.md

@@ -1,8 +1,17 @@
 # WP-10 — CIBG button fidelity
 
-Status: todo
+Status: done (<pending commit>)
 Phase: 2 — CIBG fidelity
 
+> **Deviation:** file-input's label-button was already reworked to `.btn-primary
+> .btn-upload` by the earlier out-of-order "CIBG UI fidelity pass" (WP-11/12) — the
+> vendored upload vocabulary (`.btn-upload`) supersedes this WP's original
+> `.btn-secondary` assumption, so no change was needed there. Icon affordances
+> (chevron/pijl classes) are verified present in the vendored CSS, but no in-scope
+> button (atom, file-input, RTE toolbar) currently has a next/previous affordance to
+> attach one to — skipped as not applicable, not recorded as a gap (nothing hand-rolled
+> to mark).
+
 ## Why
 
 The vendored CIBG build ships `.btn-primary / .btn-secondary / .btn-danger / .btn-ghost /
@@ -46,9 +55,9 @@ and render as unstyled Bootstrap defaults instead of CIBG buttons.
 
 ## Acceptance criteria
 
-- [ ] `grep -rn "btn-outline\|btn-sm" src/app` → empty.
-- [ ] Button story shows all CIBG variants incl. ghost; visuals match the design system.
-- [ ] Axe still green (contrast can change with real button styles).
+- [x] `grep -rn "btn-outline\|btn-sm" src/app` → empty.
+- [x] Button story shows all CIBG variants incl. ghost; visuals match the design system.
+- [x] Axe still green (contrast can change with real button styles).
 
 ## Verification