Add colored logging with shared common.sh library

- Create scripts/common.sh with reusable log() function and color definitions
- Refactor backup.sh to use common.sh for consistent logging
- Add color support: ERROR (red), WARN (yellow), SUCCESS (green), INFO (normal)
- Colors only appear in terminal, plain text in log files
- Improve code organization and DRY principle
- Fix shellcheck spacing warnings in backup.sh

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

scripts/common.sh

@@ -0,0 +1,33 @@
+# scripts/common.sh - Fonctions communes à tous les scripts
+
+# Couleurs
+RED='\033[0;31m'
+GREEN='\033[0;32m'
+YELLOW='\033[1;33m'
+BLUE='\033[0;34m'
+NC='\033[0m'
+
+# Fonction de logging
+log() {
+  local level="$1"
+  shift
+  local message="$*"
+  local timestamp
+  timestamp=$(date '+%Y-%m-%d %H:%M:%S')
+
+  local color=""
+  case "$level" in
+  ERROR) color="${RED}" ;;
+  WARN) color="${YELLOW}" ;;
+  SUCCESS) color="${GREEN}" ;;
+  INFO) color="" ;;
+  esac
+
+  echo "[$timestamp] [$level] $message" >>"${LOG_FILE:-/tmp/script.log}"
+
+  if [ -t 1 ]; then
+    echo -e "${color}[$timestamp] [$level] $message${NC}"
+  else
+    echo "[$timestamp] [$level] $message"
+  fi
+}