Add gcovr UI customization templates and build scripts

- Add HTML templates for customized gcovr coverage reports with sidebar navigation
- Add build_tree.py script to generate tree.json for directory navigation
- Add gcovr_wrapper.py for local coverage processing
- Update build.sh to handle both local/macOS and CI/Linux environments
- Add macOS workaround: auto-detect paths from .info files since gcovr cannot read .gcda files directly on macOS
- Add .gitignore for generated coverage reports and temp files

Author: julioest

.gitignore

@@ -0,0 +1,10 @@
+# Generated coverage reports
+# json/gcovr/
+# json/gcovr-lcov/
+# json/gcovr-output/
+
+# Claude Code
+.claude/
+
+# Temp files
+*.bak

build.sh

@@ -8,15 +8,51 @@ export REPONAME="json"
 export ORGANIZATION="boostorg"
 GCOVRFILTER=".*/$REPONAME/.*"
 
-cd "$REPONAME"
+SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
+cd "$SCRIPT_DIR/$REPONAME"
 BOOST_CI_SRC_FOLDER=$(pwd)
 
-cd ../boost-root
-
 outputlocation="$BOOST_CI_SRC_FOLDER/gcovr"
-outputlocation="/mnt/c/output"
 rm -rf $outputlocation || true
-
 mkdir -p $outputlocation
 
-gcovr --merge-mode-functions separate -p --html-nested --html-template-dir=..\templates --exclude-unreachable-branches --exclude-throw-branches --exclude '.*/test/.*' --exclude '.*/extra/.*' --filter "$GCOVRFILTER" --html --output "$outputlocation/index.html"
+if [[ -f "$BOOST_CI_SRC_FOLDER/coverage_filtered.info" ]]; then
+    # Local/macOS workaround: gcovr cannot read .gcda coverage files directly on macOS,
+    # so we convert the .info file (from lcov) to Cobertura XML format instead.
+    # The .info file contains absolute paths from the original build environment,
+    # which we auto-detect and rewrite to match the local machine's paths.
+    # Use 'boost-root' as anchor since it's consistently named across all builds
+    ORIGINAL_PATH=$(grep -m1 "^SF:" "$BOOST_CI_SRC_FOLDER/coverage_filtered.info" | sed 's|^SF:||' | sed 's|/boost-root/.*||')
+    TEMP_COVERAGE="/tmp/coverage_local.info"
+    TEMP_XML="/tmp/coverage.xml"
+
+    sed "s|$ORIGINAL_PATH|$SCRIPT_DIR|g" "$BOOST_CI_SRC_FOLDER/coverage_filtered.info" > "$TEMP_COVERAGE"
+    lcov_cobertura "$TEMP_COVERAGE" -o "$TEMP_XML"
+    sed -i.bak "s|filename=\"\.\./boost-root/|filename=\"$SCRIPT_DIR/boost-root/|g" "$TEMP_XML"
+
+    "$SCRIPT_DIR/scripts/gcovr_wrapper.py" \
+        --cobertura-add-tracefile "$TEMP_XML" \
+        --root "$SCRIPT_DIR" \
+        --html-nested \
+        --html-template-dir "$SCRIPT_DIR/templates/html" \
+        --output "$outputlocation/index.html"
+
+    # Generate tree.json for sidebar navigation
+    python3 "$SCRIPT_DIR/scripts/build_tree.py" "$outputlocation"
+else
+    # CI/Linux: gcovr reads coverage data directly
+    cd ../boost-root
+    gcovr --merge-mode-functions separate -p \
+        --html-nested \
+        --html-template-dir=../templates/html \
+        --exclude-unreachable-branches \
+        --exclude-throw-branches \
+        --exclude '.*/test/.*' \
+        --exclude '.*/extra/.*' \
+        --filter "$GCOVRFILTER" \
+        --html \
+        --output "$outputlocation/index.html"
+
+    # Generate tree.json for sidebar navigation
+    python3 "../scripts/build_tree.py" "$outputlocation"
+fi