chore(ci): evict stale lake-packages cache in host maintenance (#2037)

The weekly host-maintenance run prunes lake-build, compiler-ccache,
journald, and docker, but never touched /srv/verity-ci-cache/lake-packages.
That dir grows one ~5.7G entry per PR/branch/content-hash and was never
evicted, so the x64 runner root disks filled to 100% and the runners
silently dropped offline (the runner service stays active but can't write).

Add an mtime-based prune for lake-packages (default 14 days, override via
LAKE_PACKAGES_MAX_AGE_DAYS), mirroring the existing lake-build eviction.
Worst case of an over-prune is a cache miss on the next build, never
incorrectness.

Author: Th0rgal

scripts/ci_host_maintenance.sh

@@ -4,6 +4,7 @@ set -euo pipefail
 CACHE_ROOT="${CACHE_ROOT:-/srv/verity-ci-cache}"
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
 LAKE_BUILD_MAX_AGE_DAYS="${LAKE_BUILD_MAX_AGE_DAYS:-21}"
+LAKE_PACKAGES_MAX_AGE_DAYS="${LAKE_PACKAGES_MAX_AGE_DAYS:-14}"
 COMPILER_CCACHE_MAX_AGE_DAYS="${COMPILER_CCACHE_MAX_AGE_DAYS:-21}"
 ARTIFACT_MAX_AGE_HOURS="${ARTIFACT_MAX_AGE_HOURS:-24}"
 JOURNAL_VACUUM_TIME="${JOURNAL_VACUUM_TIME:-14d}"
@@ -23,6 +24,7 @@ Subcommands:
 Environment:
   CACHE_ROOT                    Default: /srv/verity-ci-cache
   LAKE_BUILD_MAX_AGE_DAYS       Default: 21
+  LAKE_PACKAGES_MAX_AGE_DAYS    Default: 14
   COMPILER_CCACHE_MAX_AGE_DAYS  Default: 21
   ARTIFACT_MAX_AGE_HOURS        Default: 24
   JOURNAL_VACUUM_TIME           Default: 14d
@@ -61,6 +63,7 @@ run_maintenance() {
 
   mkdir -p "$CACHE_ROOT"
   prune_tree "$CACHE_ROOT/lake-build" "$LAKE_BUILD_MAX_AGE_DAYS" "lake-build cache"
+  prune_tree "$CACHE_ROOT/lake-packages" "$LAKE_PACKAGES_MAX_AGE_DAYS" "lake-packages cache"
   prune_tree "$CACHE_ROOT/compiler-ccache" "$COMPILER_CCACHE_MAX_AGE_DAYS" "compiler ccache"
 
   if [ -x "$SCRIPT_DIR/ci_local_persistence.sh" ]; then