feat: add list command with global filters

internal/filters/extensions.go

@@ -0,0 +1,66 @@
+package filters
+
+import (
+	"fmt"
+	"strings"
+)
+
+// ParseExtensions converts a raw `|`-delimited extension string into a
+// normalized, deduplicated slice. Tokens must be prefixed with a dot.
+func ParseExtensions(raw string) ([]string, error) {
+	if strings.TrimSpace(raw) == "" {
+		return nil, nil
+	}
+
+	tokens := strings.Split(raw, "|")
+	seen := make(map[string]struct{}, len(tokens))
+	result := make([]string, 0, len(tokens))
+
+	for _, token := range tokens {
+		trimmed := strings.TrimSpace(token)
+		if trimmed == "" {
+			return nil, fmt.Errorf("extensions string contains empty token")
+		}
+		if !strings.HasPrefix(trimmed, ".") {
+			return nil, fmt.Errorf("extension %q must start with '.'", trimmed)
+		}
+		normalized := strings.ToLower(trimmed)
+		if _, exists := seen[normalized]; exists {
+			continue
+		}
+		seen[normalized] = struct{}{}
+		result = append(result, normalized)
+	}
+
+	return result, nil
+}
+
+// MergeExtensions merges two extension slices, deduplicating case-insensitively.
+func MergeExtensions(base, extra []string) []string {
+	if len(extra) == 0 {
+		return base
+	}
+
+	seen := make(map[string]struct{}, len(base)+len(extra))
+	merged := make([]string, 0, len(base)+len(extra))
+
+	for _, ext := range base {
+		lower := strings.ToLower(ext)
+		if _, exists := seen[lower]; exists {
+			continue
+		}
+		seen[lower] = struct{}{}
+		merged = append(merged, lower)
+	}
+
+	for _, ext := range extra {
+		lower := strings.ToLower(ext)
+		if _, exists := seen[lower]; exists {
+			continue
+		}
+		seen[lower] = struct{}{}
+		merged = append(merged, lower)
+	}
+
+	return merged
+}