Qt6 migration: Update Docker tag to ubuntu26.04 and fix submodule paths

Cosmetic changes for readability and consistency:
- Update Docker image tag from ubuntu22.04 to ubuntu26.04 in all scripts
- Align with Dockerfile base image (ubuntu:26.04)

Files updated:
- app/run_docker.sh
- migration/automate_migrate_Lts_DDS.sh
- migration/migrate_module.sh
- final-migration/run_final_migration.sh
- .github/workflows/qt6-migration.yml (submodules: recursive)
- migration/run_clang_tidy_common.sh

Documentation:
- files/qt6-submodule-migration-changes.md: Added note about qt6-after being empty

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 01M08C7DVVVDNBXGPN4M02CFB5

app/run_docker.sh

@@ -2,7 +2,7 @@
 set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
-IMAGE_NAME="${IMAGE_NAME:-migration-pipeline:ubuntu22.04}"
+IMAGE_NAME="${IMAGE_NAME:-migration-pipeline:ubuntu26.04}"
 
 CONTAINER_USER="${CONTAINER_USER:-${USER:-runner}}"
 CONTAINER_GROUP="${CONTAINER_GROUP:-$CONTAINER_USER}"