feat(scan): always scan downloads + organize dirs, deduplicate child paths

ResolveScanPaths() collects downloads.dir, organize.movies_dir,
organize.tv_shows_dir, and library.scan_path (if set), then removes
paths that are subdirectories of a parent already in the list.

This ensures the daemon and CLI scan all configured dirs without
relying solely on scan_path being set.

internal/library/paths.go

@@ -0,0 +1,55 @@
+package library
+
+import (
+	"path/filepath"
+	"strings"
+)
+
+// ResolveScanPaths returns a deduplicated list of directories to scan.
+// Always includes dlDir, moviesDir, tvDir (when non-empty).
+// Adds scanPath if non-empty.
+// Removes paths that are subdirectories of other paths in the list,
+// since a parent walk already covers them.
+func ResolveScanPaths(dlDir, moviesDir, tvDir, scanPath string) []string {
+	raw := make([]string, 0, 4)
+	for _, p := range []string{dlDir, moviesDir, tvDir, scanPath} {
+		if p != "" {
+			raw = append(raw, filepath.Clean(p))
+		}
+	}
+	return deduplicatePaths(raw)
+}
+
+// deduplicatePaths removes duplicate paths and paths that are subdirectories
+// of another path already present in the list.
+func deduplicatePaths(paths []string) []string {
+	// Remove exact duplicates first.
+	seen := make(map[string]bool, len(paths))
+	unique := make([]string, 0, len(paths))
+	for _, p := range paths {
+		if !seen[p] {
+			seen[p] = true
+			unique = append(unique, p)
+		}
+	}
+
+	// Remove paths that are subdirs of another path in the list.
+	result := make([]string, 0, len(unique))
+	for _, p := range unique {
+		isChild := false
+		for _, other := range unique {
+			if other == p {
+				continue
+			}
+			rel, err := filepath.Rel(other, p)
+			if err == nil && rel != "." && !strings.HasPrefix(rel, "..") {
+				isChild = true
+				break
+			}
+		}
+		if !isChild {
+			result = append(result, p)
+		}
+	}
+	return result
+}