refactor(ci): consolidate per-platform crow workflows into 3 matrix files

Replace 44 per-platform pipeline files with one matrix-driven file per family:
  - process-updates-<os>-<arch>.yaml (14)      -> process-updates.yaml
  - weekly-audit-missing-<os>-<arch>.yaml (16)  -> weekly-audit-missing.yaml
  - weekly-rebuild-missing-<os>-<arch>.yaml (14)-> weekly-rebuild-missing.yaml

Each file carries one matrix.include row per os/arch (the axis is named OS,
e.g. redhat-9). Runs are preserved 1:1:
  - cron: every existing per-os/arch cron still fires only its matching row,
    routed via CI_PIPELINE_CRON. Server-side cron entries are unchanged.
  - manual: a crow #1165 dropdown variable selects a single <os>-<arch> or
    "all". weekly-rebuild defaults to "all" to match its former bare manual
    trigger.

Arch placement uses the agent label as a matrix var (artemis=amd64, gaia=arm64)
for process-updates and weekly-rebuild; weekly-audit keeps arch-nodeSelector
placement. The amd64-only nodeSelector instance-type (AX42) pin is dropped in
favour of agent-based placement, and process-updates arm64 jobs now share the
same backend_options as amd64 (they previously had none).

.crow/weekly-rebuild-missing-alpine-322-arm64.yaml

@@ -1,63 +0,0 @@
-when:
-  - event: cron
-    cron: weekly-rebuild-missing-alpine-322-arm64
-  - event: manual
-
-skip_clone: true
-
-labels:
-  agent: gaia
-
-steps:
-  - name: 'Rebuild missing binaries'
-    image: reg.devxy.io/rpkgs/build-env-alpine:3.24
-    pull: true
-    environment:
-      RED_HAT_DEV_PW:
-        from_secret: RED_HAT_DEV_PW
-      B2_S3_ACCESS_KEY:
-        from_secret: B2_S3_ACCESS_KEY
-      B2_S3_SECRET_KEY:
-        from_secret: B2_S3_SECRET_KEY
-      PGPASS:
-        from_secret: PGPASS
-      REPO_RO_TOKEN:
-        from_secret: REPO_RO_TOKEN
-      GITHUB_PAT:
-        from_secret: GITHUB_PAT
-      FORGEJO_TOKEN:
-        from_secret: FORGEJO_TOKEN
-      GIT_USER: pat-s
-      R_PKG_CACHE_DIR: /mnt/cache/pkgcache
-      R_LIBS_USER: /mnt/cache/R-pkgs
-      R_VERSION: 4.5.3
-      CCACHE_DIR: /mnt/cache/ccache
-      PLATFORM: alpine-322
-      ARCH: arm64
-      NCPUS: 2
-    commands:
-      - git clone -q https://pat-s:$$REPO_RO_TOKEN@git.devxy.io/devxy/build-cran-binaries.git .
-      - mkdir -p /mnt/cache/pkgcache /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
-      - rm -rf /mnt/cache/R-pkgs/00LOCK-*
-      - /opt/R/$R_VERSION/bin/R -q -e 'if (!requireNamespace("bincraft", quietly = TRUE) || packageVersion("bincraft") != "4.2.2") pak::pak("git::https://codefloe.com/rpkgs/bincraft.git@v4.2.2")'
-      - /opt/R/$R_VERSION/bin/R -q -e 'packageVersion("bincraft")'
-      - XVFB=$(command -v xwfb-run 2>/dev/null || command -v xvfb-run); XVFB_ARGS=""; if command -v xwfb-run >/dev/null 2>&1; then dnf install -y -q weston 2>/dev/null; XVFB_ARGS="-c weston"; fi
-      - /opt/R/$R_VERSION/bin/R -q -e 'pak::pak("httr2")'
-      - /opt/R/$R_VERSION/bin/R -q -e 'source("local/fetch-rebuild-packages-from-issue.R")'
-      - $XVFB $XVFB_ARGS -- /opt/R/$R_VERSION/bin/R -q -e "sink(stdout(), type = 'message'); options(crayon.enabled = TRUE, Ncpus = $NCPUS, future.globals.onReference = NULL); pkgs <- readLines('/tmp/rebuild_pkgs.txt'); if (length(pkgs) == 0) { cat('Nothing to rebuild\n'); q('no') }; excluded <- jsonlite::fromJSON('local/excluded-packages.json')[['package']]; pkgs <- setdiff(pkgs, excluded); cat(sprintf('Rebuilding %d packages\n', length(pkgs))); n <- length(pkgs); for (i in seq_along(pkgs)) { x <- pkgs[i]; cat(sprintf('[%d/%d] %s\n', i, n, x)); tryCatch(bincraft::build_binary_package(x, tag_limit = 1L, s3_endpoint = 'https://s3.eu-central-003.backblazeb2.com', s3_region = 'eu-central-003', s3_bucket = 'devxy-rpkgs-binaries', s3_access_key_id = Sys.getenv('B2_S3_ACCESS_KEY'), s3_secret_access_key = Sys.getenv('B2_S3_SECRET_KEY'), metadata_db_host = 'r-binaries.devxy.io', metadata_db_name = 'build_metadata', metadata_db_table = 'single_builds', metadata_db_user = 'rpkgs', metadata_db_password = Sys.getenv('PGPASS'), metadata_db_sslmode = 'require', metadata_db_port = 15432, archive = TRUE, upload = TRUE, store_build_metadata = TRUE), error = function(e) cat(sprintf('ERROR building %s - %s\n', x, conditionMessage(e)))) }" 2>&1
-    backend_options:
-      kubernetes:
-        resources:
-          requests:
-            memory: 5Gi
-            cpu: 3000m
-          limits:
-            memory: 18Gi
-            cpu: 3000m
-        nodeSelector:
-          kubernetes.io/arch: arm64
-        tolerations:
-          - key: 'CI'
-            operator: 'Equal'
-            value: 'true'
-            effect: 'NoSchedule'