[IMP] avoid directory changes in migration loop

Replace cd into version directories with absolute path execution:

Before:
  cd "${version}.0"
  ./pre_upgrade.sh
  ./upgrade.sh
  ./post_upgrade.sh
  cd ..

After:
  "${SCRIPT_DIR}/${version}.0/pre_upgrade.sh"
  "${SCRIPT_DIR}/${version}.0/upgrade.sh"
  "${SCRIPT_DIR}/${version}.0/post_upgrade.sh"

Benefits:
- No working directory state to track
- More robust: script works regardless of where it's called from
- Easier debugging: no need to remember current directory
- Avoids potential issues if a subscript changes directory

upgrade.sh

@@ -125,13 +125,10 @@ log_step "UPGRADE PROCESS"
 for version in "${versions[@]}"; do
     log_info "START UPGRADE TO ${version}.0"
 
-    cd "${version}.0"
+    "${SCRIPT_DIR}/${version}.0/pre_upgrade.sh"
+    "${SCRIPT_DIR}/${version}.0/upgrade.sh"
+    "${SCRIPT_DIR}/${version}.0/post_upgrade.sh"
 
-    ./pre_upgrade.sh
-    ./upgrade.sh
-    ./post_upgrade.sh
-
-    cd ..
     log_info "END UPGRADE TO ${version}.0"
 done