Session 025: Update MIGRATION_STATUS.md with QTextCodec fixes

Document Session 025 changes:
- QTextCodec include path fixes (QtCore → QtGui)
- Qt6::Gui dependency added for qsql_informix
- Qt::codecForHtml → QTextCodec::codecForHtml migration

Co-authored-by: Copilot <2235566219+Copilot@users.noreply.github.com>
Entire-Checkpoint: 01M0WXBCWW3ZRK04T710CVB0JM

MIGRATION_STATUS.md

@@ -1,5 +1,50 @@
 # Qt5/C++11 → Qt6/C++17 Migration Status
 
+## Session 025: QTextCodec Migration Fixes (2026-08-24)
+
+### ✅ QTextCodec Qt6 Compatibility Fixes
+
+Fixed QTextCodec-related migration issues in Z and Lts/Tools modules:
+
+**Files Updated:**
+1. **Z/src/qsql_informix/qsql_informix.cpp**
+   - Line 24: Fixed include path `#include <QtCore/QTextCodec>` → `#include <QtGui/QTextCodec>`
+   - QTextCodec moved from QtCore to QtGui module in Qt6
+
+2. **Z/src/qsql_informix/CMakeLists.txt**
+   - Added `Qt6::Gui` dependency to TARGET_LINK_LIBRARIES
+   - Required for QTextCodec functionality in Qt6
+
+3. **Lts/Tools/TextEditorTest/textedit.cpp**
+   - Line 370: Fixed `Qt::codecForHtml(data)` → `QTextCodec::codecForHtml(data)`
+   - In Qt6, codecForHtml is a static method on QTextCodec class, not Qt namespace function
+
+**Technical Details:**
+- QTextCodec relocation: QtCore (Qt5) → QtGui (Qt6)
+- API change: `Qt::codecForHtml()` → `QTextCodec::codecForHtml()` (static method)
+- Both changes are minimal, required for Qt6 compatibility
+- No behavioral changes, semantics preserved
+
+**Verification:**
+```bash
+$ grep -r "Qt::codecForHtml" qt6-after/qt6-migrated-legatus/ --include="*.cpp"
+# Zero results - all instances migrated
+
+$ grep -r "QTextCodec" qt6-after/qt6-migrated-legatus/ --include="*.cpp" | grep -v "//"
+# 2 files with valid QTextCodec usage (qsql_informix.cpp, textedit.cpp)
+```
+
+**Remaining QTextCodec Usage:**
+- `Z/src/qsql_informix/qsql_informix.cpp`: Database locale encoding (QTextCodec::codecForName)
+- `Lts/Tools/TextEditorTest/textedit.cpp`: HTML encoding detection (QTextCodec::codecForHtml)
+- Both are Qt6-compatible with QtGui module linkage
+
+**Commits:**
+- Submodule: `c143ff8a4` (Session 025: Fix QTextCodec migration issues)
+- Main repo: Pending (submodule reference update)
+
+---
+
 ## Session 024: Qt5:: CMake References Cleanup Complete (2026-08-24)
 
 ### ✅ All Qt5:: CMake References Migrated to Qt6::