Add color code bug prevention: cecho helper + coding guidelines

PREVENTION STRATEGY for "echo without -e" bug:

1. NEW HELPER FUNCTION - cecho()
   - Added to lib/common-functions.sh (lines 100-115)
   - Wrapper around echo -e for colored output
   - Clear documentation with examples
   - Usage: cecho "${BOLD}Text${NC}" instead of echo -e

2. COMPREHENSIVE CODING GUIDELINES
   - Created CODING_GUIDELINES.md
   - Documents the echo -e color bug with examples
   - Prevention rules and quick reference table
   - Search command to find potential issues
   - Pre-commit checklist for developers
   - Performance guidelines (subprocess elimination)

3. DOCUMENTATION INCLUDES:
   - Why the bug happens (escape sequences not interpreted)
   - How to identify it (grep pattern)
   - How to fix it (echo -e or cecho)
   - When to use each approach
   - Historical context (commit 7053b3b)

BENEFITS:
- Future developers can reference guidelines
- cecho() provides cleaner, safer API
- Search pattern helps audit existing code
- Reduces recurring "This happens a lot" issues

USER FEEDBACK ADDRESSED:
User: "This happens a lot with you. is there a way for us to avoid this in the future?"
Answer: Yes - cecho() helper + guidelines document + search pattern

lib/common-functions.sh

@@ -97,6 +97,23 @@ print_header() {
     echo -e "${CYAN}${BOLD}$1${NC}"
 }
 
+#############################################################################
+# Color Echo Helper - ALWAYS use this when printing colored text
+#
+# PROBLEM: Using 'echo' without -e flag doesn't interpret escape sequences
+# BAD:  echo "  ${BOLD}1${NC} - Menu option"     → Shows: \033[1m1\033[0m
+# GOOD: cecho "  ${BOLD}1${NC} - Menu option"    → Shows: 1 (bold)
+#
+# USAGE:
+#   cecho "Normal text with ${RED}colored${NC} parts"
+#   cecho "${BOLD}Bold text${NC}"
+#
+# WHY: Prevents common bug where color codes show as literal text
+#############################################################################
+cecho() {
+    echo -e "$@"
+}
+
 # Wait for user input
 press_enter() {
     echo ""