[ci] add JSON validation CI workflow (#5837)

## Summary

Added GitHub Actions workflow and shell script to validate JSON syntax
in repository files, as in the past we have committed locales files with
invalid JSON.

## Changes

- **What**: Added CI workflow for JSON validation with `jq` syntax
checking
- **Dependencies**: CI workflow requires `jq` (pre-installed on
ubuntu-latest runners)

## Review Focus

Script exclusion patterns for TSConfig files and environment variable
override mechanism (`JSON_LINT_EXCLUDES`).

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-5837-ci-add-JSON-validation-CI-workflow-27c6d73d365081a199b1d9ae9e4edfa4)
by [Unito](https://www.unito.io)

Author: christian-byrne

.github/workflows/json-validate.yaml

@@ -0,0 +1,15 @@
+name: Validate JSON
+
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+
+jobs:
+  json-lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - name: Validate JSON syntax
+        run: ./scripts/cicd/check-json.sh

scripts/cicd/check-json.sh

@@ -0,0 +1,77 @@
+#!/bin/bash
+set -euo pipefail
+
+usage() {
+  echo "Usage: $0 [--debug]" >&2
+}
+
+debug=0
+
+while [ "$#" -gt 0 ]; do
+  case "$1" in
+    --debug)
+      debug=1
+      ;;
+    -h|--help)
+      usage
+      exit 0
+      ;;
+    *)
+      echo "Unknown option: $1" >&2
+      usage
+      exit 2
+      ;;
+  esac
+  shift
+done
+
+# Validate JSON syntax in tracked files using jq
+if ! command -v jq >/dev/null 2>&1; then
+  echo "Error: jq is required but not installed" >&2
+  exit 127
+fi
+
+EXCLUDE_PATTERNS=(
+  '**/tsconfig*.json'
+)
+
+if [ -n "${JSON_LINT_EXCLUDES:-}" ]; then
+  # shellcheck disable=SC2206
+  EXCLUDE_PATTERNS+=( ${JSON_LINT_EXCLUDES} )
+fi
+
+pathspecs=(-- '*.json')
+for pattern in "${EXCLUDE_PATTERNS[@]}"; do
+  if [[ ${pattern:0:1} == ':' ]]; then
+    pathspecs+=("$pattern")
+  else
+    pathspecs+=(":(glob,exclude)${pattern}")
+  fi
+done
+
+mapfile -t json_files < <(git ls-files "${pathspecs[@]}")
+
+if [ "${#json_files[@]}" -eq 0 ]; then
+  echo 'No JSON files found.'
+  exit 0
+fi
+
+if [ "$debug" -eq 1 ]; then
+  echo 'JSON files to validate:'
+  printf '  %s\n' "${json_files[@]}"
+fi
+
+failed=0
+for file in "${json_files[@]}"; do
+  if ! jq -e . "$file" >/dev/null; then
+    echo "Invalid JSON syntax: $file" >&2
+    failed=1
+  fi
+done
+
+if [ "$failed" -ne 0 ]; then
+  echo 'JSON validation failed.' >&2
+  exit 1
+fi
+
+echo 'All JSON files are valid.'