fix(builder): bump test versions to next patch

After a stable tag vX.Y.Z, untagged commits now produce
X.Y.(Z+1)~date.branch.n+gSHA so test DEBs sort above the last
official release and still below the next official X.Y.(Z+1).

skills/builder/scripts/version.sh

@@ -11,7 +11,7 @@ With --docker, print the Docker tag rendering of that version.
 
 Derivation (builder contract «版本号»):
   official  HEAD exact-match of vX.Y.Z          → X.Y.Z
-  test      nearest ancestor stable tag         → X.Y.Z~YYYYMMDD.branch.n+gSHA
+  test      nearest ancestor stable tag vX.Y.Z  → X.Y.(Z+1)~YYYYMMDD.branch.n+gSHA
   no tag    no stable tag reachable from HEAD   → 0.0.0~YYYYMMDD.branch+gSHA
 
 YYYYMMDD is the build date. SOURCE_DATE_EPOCH, if set, is that instant in
@@ -62,6 +62,15 @@ is_official_version() {
   [[ "$1" =~ ^[0-9]+\.[0-9]+\.[0-9]+$ ]]
 }
 
+# Mechanical sort key: next patch of a stable tag / X.Y.Z version.
+# v1.2.0 → 1.2.1. Not a claim that the next official release is 1.2.1.
+bump_patch() {
+  local v=$1 major minor patch
+  v=${v#v}
+  IFS=. read -r major minor patch <<<"$v"
+  printf '%s.%s.%s' "$major" "$minor" "$((10#$patch + 1))"
+}
+
 # Strip one leading v if present.
 strip_v() {
   local v=$1
@@ -163,7 +172,7 @@ derive_canonical() {
     return
   fi
   n=$(gitc rev-list --count "${base}..HEAD")
-  printf '%s~%s.%s.%s+g%s' "${base#v}" "$ymd" "$branch" "$n" "$sha"
+  printf '%s~%s.%s.%s+g%s' "$(bump_patch "$base")" "$ymd" "$branch" "$n" "$sha"
 }
 
 to_docker() {