refactor: improve code quality and test coverage

This commit addresses several code quality issues identified in the
recent bash 3.2 compatibility fixes:

1. Remove redundant array length check in is_whitelisted()
   - The second check for array length > 0 is unnecessary after
     already checking for length == 0

2. Clean up commented dangerous cleanup code in dev.sh
   - Replace commented-out code with clear documentation
   - Add explicit notes explaining why certain paths are excluded
   - Improves maintainability by preventing confusion

3. Enhance test coverage for excluded paths
   - Add tests to verify Mix archives are NOT cleaned
   - Add tests to verify Stack programs are NOT cleaned
   - Add tests to verify VS Code workspace storage is NOT cleaned
   - These tests ensure critical data remains protected

All changes pass ShellCheck, syntax validation, and formatting checks.

lib/manage/whitelist.sh

@@ -248,15 +248,13 @@ is_whitelisted() {
         return 1
     fi
 
-    if [[ ${#CURRENT_WHITELIST_PATTERNS[@]} -gt 0 ]]; then
-        for existing in "${CURRENT_WHITELIST_PATTERNS[@]}"; do
-            local existing_expanded="${existing/#\~/$HOME}"
-            # Only use exact string match to prevent glob expansion security issues
-            if [[ "$check_pattern" == "$existing_expanded" ]]; then
-                return 0
-            fi
-        done
-    fi
+    for existing in "${CURRENT_WHITELIST_PATTERNS[@]}"; do
+        local existing_expanded="${existing/#\~/$HOME}"
+        # Only use exact string match to prevent glob expansion security issues
+        if [[ "$check_pattern" == "$existing_expanded" ]]; then
+            return 0
+        fi
+    done
     return 1
 }