build(grantlee): add Qt6 migration helper script build_grantlee_qt6.sh to attempt pragmatic CMake patches and build against Qt6

app/build_grantlee_qt6.sh

@@ -0,0 +1,57 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+# build_grantlee_qt6.sh - build grantlee with pragmatic Qt6 patches and install to INSTALL_PREFIX
+QT_ROOT=${QT_ROOT:-/opt/Qt/6.8.3/gcc_64}
+INSTALL_PREFIX=${INSTALL_PREFIX:-/usr/local}
+
+echo "Building Grantlee (attempt Qt6 port) into ${INSTALL_PREFIX} using QT_ROOT=${QT_ROOT}"
+TMPDIR=$(mktemp -d)
+trap 'rm -rf "$TMPDIR"' EXIT
+cd "$TMPDIR"
+
+if ! git clone --depth 1 https://github.com/steveire/grantlee.git grantlee; then
+  echo "Failed to clone grantlee" >&2
+  exit 1
+fi
+
+pushd grantlee >/dev/null
+# Backup relevant files
+git ls-files | grep -E "CMakeLists.txt|\\.cmake$" | xargs -r -n1 -I{} cp {} {}.bak || true
+
+# Python-based safe patches
+python3 - <<'PY'
+import re
+from pathlib import Path
+patterns = [
+  (re.compile(r'find_package\s*\(\s*Qt5[^)]*\)', re.M), 'find_package(Qt6 REQUIRED COMPONENTS Core Widgets)'),
+  (re.compile(r'Qt5::'), 'Qt6::'),
+  (re.compile(r'QT5_WRAP_CPP'), 'QT_WRAP_CPP'),
+]
+for p in Path('.').rglob('*'):
+    if p.is_file() and (p.name=='CMakeLists.txt' or p.suffix=='.cmake'):
+        try:
+            s = p.read_text()
+            orig = s
+            for pat, repl in patterns:
+                s = pat.sub(repl, s)
+            if s != orig:
+                p.write_text(s)
+                print('Patched', p)
+        except Exception as e:
+            print('Skipping', p, 'error', e)
+PY
+
+popd >/dev/null
+
+mkdir -p grantlee/build
+cd grantlee/build
+cmake -DCMAKE_BUILD_TYPE=Release \
+      -DCMAKE_INSTALL_PREFIX="${INSTALL_PREFIX}" \
+      -DCMAKE_PREFIX_PATH="${QT_ROOT}:${INSTALL_PREFIX}" ..
+
+cmake --build . -- -j$(nproc) || true
+cmake --install . || true
+
+echo "Grantlee attempted build finished"
+exit 0