refactor(ci): consolidate build-all-versions workflows (4 -> 2 files)

Merge the per-arch build-all and install-deps files into one each:
  build-all-versions-{amd64,arm64}.yaml             -> build-all-versions.yaml
  build-all-versions-install-deps-{amd64,arch}.yaml -> build-all-versions-install-deps.yaml

Arch becomes a matrix axis carrying the per-arch agent (artemis/gaia),
BACKEND (kubernetes/docker) and R_PKG_CACHE_DIR. Routing is unchanged: the
existing `task == "build-all-${ARCH}"` selector means
`--var task=build-all-amd64` still runs only the amd64 rows. OS / OS_VERSION /
R_VERSION / K8S_INSTANCE_TYPE are still passed via --var. These pipelines are
manual-only (no cron).

.crow/build-all-versions-install-deps.yaml

@@ -0,0 +1,68 @@
+# Consolidated install-deps for build-all (both arches in one file).
+# Arch is a matrix axis; the existing task selector still routes it:
+#   task == "build-all-amd64" runs the amd64 row, "build-all-arm64" the arm64 row.
+# OS / OS_VERSION / R_VERSION / K8S_INSTANCE_TYPE are still passed via --var.
+when:
+  - event: manual
+    evaluate: 'task == "build-all-${ARCH}"'
+
+skip_clone: true
+
+labels:
+  platform: linux/${ARCH}
+  agent: ${AGENT}
+
+matrix:
+  include:
+    - ARCH: amd64
+      AGENT: artemis
+    - ARCH: arm64
+      AGENT: gaia
+
+steps:
+  - name: 'Install deps and bincraft'
+    image: 'reg.devxy.io/rpkgs/build-env-${OS}:${OS_VERSION}'
+    pull: true
+    environment:
+      REPO_RO_TOKEN:
+        from_secret: REPO_RO_TOKEN
+      GITHUB_PAT:
+        from_secret: GITHUB_PAT
+      B2_S3_ACCESS_KEY:
+        from_secret: B2_S3_ACCESS_KEY
+      B2_S3_SECRET_KEY:
+        from_secret: B2_S3_SECRET_KEY
+      PGPASS:
+        from_secret: PGPASS
+      R_PKG_CACHE_DIR: /mnt/cache/pkgcache
+      R_LIBS_USER: /mnt/cache/R-pkgs
+      CCACHE_DIR: /mnt/cache/ccache
+    volumes:
+      - ${ARCH}-binaries-r-dep-cache-${OS}-${OS_VERSION//./}:/mnt/cache
+    commands:
+      # one-time full wipe to fix corrupted .so files from previous failed builds
+      # - rm -rf /mnt/cache/R-pkgs
+      - mkdir -p /mnt/cache/pkgcache /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
+      - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
+      - git clone -q https://codefloe.com/rpkgs/bincraft.git /tmp/bincraft
+      - /opt/R/$R_VERSION/bin/R -q -e 'pak::sysreqs_db_update(); pak::local_install("/tmp/bincraft"); pak::pak(c("RPostgres", "s3fs", "data.table", "future", "jsonlite")); packageVersion("bincraft")'
+      - /opt/R/$R_VERSION/bin/R -q -e "source('local/packages-to-build.R'); saveRDS(pkgs, '/mnt/cache/packages/pkgs_to_build.rds'); saveRDS(pkgs[r_minor_sensitive == TRUE], '/mnt/cache/packages/r_minor_sensitive_pkgs.rds'); sprintf('Precomputed %s package versions (%s r-minor-sensitive)', nrow(pkgs), nrow(pkgs[r_minor_sensitive == TRUE]))"
+    backend_options:
+      docker:
+        resources:
+          requests:
+            memory: 5Gi
+            cpu: 1000m
+      kubernetes:
+        resources:
+          requests:
+            memory: 5Gi
+            cpu: 1000m
+        nodeSelector:
+          kubernetes.io/arch: ${ARCH}
+          node.kubernetes.io/instance-type: ${K8S_INSTANCE_TYPE}
+        tolerations:
+          - key: 'CI'
+            operator: 'Equal'
+            value: 'true'
+            effect: 'NoSchedule'