fix(shell-docs): correct REB2B var name (was RB2B_ID, code reads REB2B_KEY)

The previous commit used `NEXT_PUBLIC_RB2B_ID` based on a stale entry
in the cutover plan doc, but `app/layout.tsx:86` reads
`NEXT_PUBLIC_REB2B_KEY`. Without this fix the build-arg would be
piped under the wrong name and the REB2B Script tag would still not
render.

Author: samjulien

.github/workflows/showcase_build.yml

@@ -304,7 +304,7 @@ jobs:
             # inlined into client JS chunks. Sourced from repo secrets;
             # Railway runtime env doesn't reach this build step.
             ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_POSTHOG_KEY=${{ secrets.POSTHOG_PROJECT_KEY }}"
-            ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_RB2B_ID=${{ secrets.RB2B_ID }}"
+            ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_REB2B_KEY=${{ secrets.REB2B_KEY }}"
             ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_SCARF_PIXEL_ID=${{ secrets.SCARF_PIXEL_ID }}"
             ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_REO_KEY=${{ secrets.REO_PROJECT_KEY }}"
             ARGS="${ARGS:+${ARGS}$'\n'}NEXT_PUBLIC_GOOGLE_ANALYTICS_TRACKING_ID=${{ secrets.GOOGLE_ANALYTICS_TRACKING_ID }}"

showcase/shell-docs/Dockerfile

@@ -12,8 +12,8 @@ ENV NEXT_PUBLIC_BASE_URL=${NEXT_PUBLIC_BASE_URL}
 # no-op in the browser.
 ARG NEXT_PUBLIC_POSTHOG_KEY
 ENV NEXT_PUBLIC_POSTHOG_KEY=${NEXT_PUBLIC_POSTHOG_KEY}
-ARG NEXT_PUBLIC_RB2B_ID
-ENV NEXT_PUBLIC_RB2B_ID=${NEXT_PUBLIC_RB2B_ID}
+ARG NEXT_PUBLIC_REB2B_KEY
+ENV NEXT_PUBLIC_REB2B_KEY=${NEXT_PUBLIC_REB2B_KEY}
 ARG NEXT_PUBLIC_SCARF_PIXEL_ID
 ENV NEXT_PUBLIC_SCARF_PIXEL_ID=${NEXT_PUBLIC_SCARF_PIXEL_ID}
 ARG NEXT_PUBLIC_REO_KEY