fix(cdn): align repository routing across pull zones (#165)

## Motivation

`cran.rpkgs.com` and `cran.allianceswisspass.devxy.io` serve the same B2 repository through separate Bunny pull zones, but only the first zone was managed and purged after weekly reindexing.
This allowed the Alliance endpoint to retain stale repository metadata and left locked `renv` restores unable to retrieve versions whose binary archive object was absent.

## Changes

- Adopt the Alliance SwissPass pull zone `3265648` into OpenTofu and configure it with the shared B2 origin and middleware script.
- Purge both Bunny pull zones after the weekly rebuild reindex.
- Preserve the requested public hostname in middleware redirects.
- Redirect missing archived binaries to the corresponding CRAN source package, checking whether the version is archived or still current.
- Cover the existing archived-binary passthrough behavior in the edge routing matrix.

## Verification

- `prek run -a`
- `just edge-test`
- `crow lint .crow/`
- `tofu validate`
- `bash -n scripts/purge_cdn_zone.sh`

## Deployment

Run `tofu apply` to adopt pull zone `3265648`, publish the middleware release, and align both pull zones.
After the apply, rerun the Alliance SwissPass CI restore that requested `cli 3.6.5` and `AzureStor 3.7.1`.

Reviewed-on: #165

.crow/weekly-rebuild-reindex.yaml

@@ -173,13 +173,13 @@ steps:
       OTEL_R_METRICS_EXPORTER: none
       BUNNYNET_API_KEY:
         from_secret: BUNNYNET_API_KEY
-      # All hostnames on the zone share this id, so one purge covers
-      # cran.devxy.io, cran.allianceswisspass.devxy.io and cran.rpkgs.com.
-      BUNNY_PULLZONE: '3857050'
+      # cran.rpkgs.com and cran.allianceswisspass.devxy.io are on separate
+      # Bunny pull zones, so both must be purged after the shared origin changes.
+      BUNNY_PULLZONES: '3857050 3265648'
     commands:
       - apk add --no-cache -q bash curl
       # Crow carries the checkout from the re-index step into this step.
-      - bash scripts/purge_cdn_zone.sh "$BUNNYNET_API_KEY" "$BUNNY_PULLZONE"
+      - bash scripts/purge_cdn_zone.sh "$BUNNYNET_API_KEY" $BUNNY_PULLZONES
     # Runs on every row rather than on one designated slot: a cron fires only
     # its own slot's row, so gating on a named slot would leave every other
     # slot unpurged. A manual "all" run therefore purges the zone 18 times,