refactor: migrate package installation from pak to uvr

bincraft dropped pak in favour of uvr, so the pipelines, helper scripts
and images in this repo move with it.

- add local/uvr-install.sh as the single replacement for pak::pak(); it
  bootstraps a pinned uvr, mints a throwaway project under TMPDIR and
  runs `uvr add --no-install` + `uvr sync --library`, because `uvr add`
  refuses to run outside a project and only `sync` honours --library
- install bincraft via its Forgejo spec (forgejo::codefloe.com/rpkgs/
  bincraft@<tag>) instead of a git:: URL, keeping the git ls-remote tag
  resolution
- pass UVR_R_BIN/UVR_TARGET_LIB from install-bincraft.R so the
  per-R-minor passes target their own R and library
- replace R_PKG_CACHE_DIR with UVR_CACHE_DIR/UVR_PACKAGES_DIR on the
  persistent volume, preserving the amd64-off/arm64-on split
- drop trim_pkgcache_metadata() and its test; uvr's cache does not grow
  the way pkgcache's _metadata dir did
- let uvr install system requirements from its vendored
  r-system-requirements rules, replacing pak::sysreqs_db_update()
- migrate the shiny app image, the alpine reprex and the CRAN loading
  test; ship uvr-install.sh in the build-one image
- track the uvr pin with renovate

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

@@ -10,22 +10,22 @@ variables:
       - arm64
     default: amd64
   OS:
-    description: "Base OS image name."
+    description: 'Base OS image name.'
     options:
       - alpine
       - redhat
       - ubuntu
     default: alpine
   OS_VERSION:
-    description: "OS image tag. Must match OS (alpine: 3.24; redhat: 8/9/10; ubuntu: jammy/noble)."
+    description: 'OS image tag. Must match OS (alpine: 3.24; redhat: 8/9/10; ubuntu: jammy/noble).'
     options:
-      - "3.24"
-      - "8"
-      - "9"
-      - "10"
-      - "jammy"
-      - "noble"
-    default: "3.24"
+      - '3.24'
+      - '8'
+      - '9'
+      - '10'
+      - 'jammy'
+      - 'noble'
+    default: '3.24'
   R_VERSION:
     description: 'Primary R version under /opt/R.'
     options:
@@ -66,23 +66,24 @@ steps:
         from_secret: B2_S3_SECRET_KEY
       PGPASS:
         from_secret: PGPASS
-      R_PKG_CACHE_DIR: /mnt/cache/pkgcache
       R_LIBS_USER: /mnt/cache/R-pkgs
+      # Keep uvr's downloads and extracted-package entries on the persistent
+      # volume instead of the container-local ~/.uvr default.
+      UVR_CACHE_DIR: /mnt/cache/uvr/cache
+      UVR_PACKAGES_DIR: /mnt/cache/uvr/packages
       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
-      # Clear churny pkgcache metadata left by a prior crashed run (the "patched"
-      # repo mints a new hash per PACKAGES change -> unbounded pkgs-*.rds/patched-*).
-      # Keep pkg/ downloads and the stable CRAN/BioC/INLA repo dirs.
-      - rm -rf /mnt/cache/pkgcache/R/pkgcache/_metadata/patched-* /mnt/cache/pkgcache/R/pkgcache/_metadata/pkgs-*.rds || true
-      - mkdir -p /mnt/cache/pkgcache /mnt/cache/R-pkgs /mnt/cache/ccache /mnt/cache/packages
+      - mkdir -p /mnt/cache/uvr/cache /mnt/cache/uvr/packages /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 .
       # Pin the same bincraft version the build steps use, so the precomputed
       # snapshot and the per-agent library stay consistent across the pipeline.
-      - /opt/R/$R_VERSION/bin/R -q -e 'pak::sysreqs_db_update(); source("local/install-bincraft.R"); pak::pak(c("RPostgres", "s3fs", "data.table", "future", "jsonlite")); packageVersion("bincraft")'
+      - /opt/R/$R_VERSION/bin/Rscript local/install-bincraft.R
+      - UVR_R_BIN=/opt/R/$R_VERSION/bin/R local/uvr-install.sh RPostgres s3fs data.table future jsonlite
+      - /opt/R/$R_VERSION/bin/R -q -e '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: