fix(openbao-ui): handle OIDC callback without Ember popup flow

OpenBao's Ember UI expects OIDC to complete in a popup and postMessage to
window.opener. The standalone KeyCape login uses a full-page redirect, so the
callback now exchanges the authorization code directly, persists the UI token
in localStorage, and redirects into the vault UI. Unauthenticated /ui/ loads
also redirect to the standalone login page to avoid ?with= bounce loops.

scripts/openbao-ui-overlay-apply.sh

@@ -27,7 +27,7 @@ if [ "${1:-}" = "-h" ] || [ "${1:-}" = "--help" ]; then
   exit 0
 fi
 
-for required in overlay.css overlay.js login.css login.html login.js presets.json nginx.conf VERSION; do
+for required in overlay.css overlay.js callback.html callback.js login.css login.html login.js presets.json nginx.conf VERSION; do
   if [ ! -f "$OVERLAY_DIR/$required" ]; then
     echo "missing overlay asset: $OVERLAY_DIR/$required" >&2
     exit 1
@@ -47,6 +47,8 @@ $KUBECTL create configmap openbao-ui-overlay \
   --namespace "$OPENBAO_NAMESPACE" \
   --from-file="$OVERLAY_DIR/overlay.css" \
   --from-file="$OVERLAY_DIR/overlay.js" \
+  --from-file="$OVERLAY_DIR/callback.html" \
+  --from-file="$OVERLAY_DIR/callback.js" \
   --from-file="$OVERLAY_DIR/login.css" \
   --from-file="$OVERLAY_DIR/login.html" \
   --from-file="$OVERLAY_DIR/login.js" \