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

migration/automate_migrate_Lts_DDS.sh

@@ -2,7 +2,7 @@
 set -euo pipefail
 
 # automate_migrate_Lts_DDS.sh
-# Run inside migration Docker image (migration-pipeline:ubuntu22.04)
+# Run inside migration Docker image (migration-pipeline:ubuntu26.04)
 # - Installs lightweight tooling (clang-tidy, clang-format, pip)
 # - Runs clang-tidy fixes (safe checks) over Lts/DDS
 # - Runs strix to generate tests for modified functions (if strix available)