feat(smartplaylist): per-playlist refreshDelay for stable daily/weekly playlists (#5790)

* feat(utils): add ParseDuration/FormatDuration with day and week units

* feat(criteria): add per-playlist refreshDelay to smart playlist rules

* feat(smartplaylist): honor per-playlist refreshDelay in refresh gate

* feat(subsonic): compute smart playlist validUntil from effective refresh delay

* fix(playlists): reset smart playlist evaluation window when rules change via API

* refactor(utils): flatten FormatDuration recursion, single-pass duration regex

* fix(playlists): address PR review feedback

- Reset EvaluatedAt to nil instead of zero-time on rules change and NSP
  re-import, so getPlaylist(s) never reports year-1 Changed/validUntil in
  the window between an edit and the next owner read
- Parse negative d/w durations so they are rejected with the consistent
  "negative duration" error instead of "unknown unit"
- Quote input in the negative-duration error, matching the parse error
- Gate per-playlist RefreshDelay behind IsSmartPlaylist, matching its doc

core/playlists/import.go

@@ -8,7 +8,6 @@ import (
 	"os"
 	"path/filepath"
 	"strings"
-	"time"
 
 	"github.com/navidrome/navidrome/conf"
 	"github.com/navidrome/navidrome/log"
@@ -187,7 +186,7 @@ func (s *playlists) updatePlaylist(ctx context.Context, newPls *model.Playlist,
 		newPls.OwnerID = pls.OwnerID
 		newPls.Public = pls.Public
 		newPls.UploadedImage = pls.UploadedImage // Preserve manual upload
-		newPls.EvaluatedAt = &time.Time{}
+		newPls.EvaluatedAt = nil                 // force re-evaluation on next read
 	} else {
 		log.Info(ctx, "Adding synced playlist", "playlist", newPls.Name, "path", newPls.Path, "owner", owner.UserName)
 		newPls.OwnerID = owner.ID

core/playlists/rest_adapter.go

@@ -135,6 +135,7 @@ func (s *playlists) applyContentUpdate(ctx context.Context, current, entity *mod
 	}
 	if rulesChanged {
 		current.Rules = entity.Rules
+		current.EvaluatedAt = nil // force re-evaluation on next read
 	}
 	if sent("sync") && current.Path != "" && current.Sync != entity.Sync {
 		current.Sync = entity.Sync

core/playlists/rest_adapter_test.go

@@ -314,6 +314,38 @@ var _ = Describe("REST Adapter", func() {
 					Expect(mockPlsRepo.Last.Public).To(BeTrue())
 				})
 
+				It("resets EvaluatedAt when rules change", func() {
+					evaluatedAt := time.Now().Add(-1 * time.Hour)
+					mockPlsRepo.Data["smart-reset"] = &model.Playlist{
+						ID:          "smart-reset",
+						Name:        "Smart",
+						OwnerID:     "user-1",
+						Rules:       &criteria.Criteria{Expression: criteria.Is{"genre": "Rock"}},
+						EvaluatedAt: &evaluatedAt,
+					}
+					repo = ps.NewRepository(ctx).(rest.Persistable)
+					newRules := &criteria.Criteria{Expression: criteria.Is{"genre": "Jazz"}}
+					err := repo.Update("smart-reset", &model.Playlist{Rules: newRules}, "rules")
+					Expect(err).ToNot(HaveOccurred())
+					Expect(mockPlsRepo.Last.EvaluatedAt).To(BeNil())
+				})
+
+				It("keeps EvaluatedAt when rules are not changed", func() {
+					evaluatedAt := time.Now().Add(-1 * time.Hour)
+					mockPlsRepo.Data["smart-keep"] = &model.Playlist{
+						ID:          "smart-keep",
+						Name:        "Smart",
+						OwnerID:     "user-1",
+						Rules:       &criteria.Criteria{Expression: criteria.Is{"genre": "Rock"}},
+						EvaluatedAt: &evaluatedAt,
+					}
+					repo = ps.NewRepository(ctx).(rest.Persistable)
+					err := repo.Update("smart-keep", &model.Playlist{Name: "Renamed Smart"}, "name")
+					Expect(err).ToNot(HaveOccurred())
+					Expect(mockPlsRepo.Last.EvaluatedAt).ToNot(BeNil())
+					Expect(*mockPlsRepo.Last.EvaluatedAt).To(BeTemporally("~", evaluatedAt, time.Second))
+				})
+
 				It("updates name and rules together (smart-playlist Edit form)", func() {
 					mockPlsRepo.Data["smart-edit"] = &model.Playlist{
 						ID:      "smart-edit",