chore(preferences): drop the dead sync group

sync.enabled/sync.interval-minutes were declared, visible and
editable in the schema, but nothing in the codebase ever read them --
no scheduler, no LibrarySyncTask config, nothing. Removed the group
from preferences.yaml, its entry from SettingsView.GROUP_ORDER, and
the now-orphaned settings.group.sync/settings.sync.* labels from both
message bundles.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

src/main/java/org/icroco/pholio/ui/shell/SettingsView.java

@@ -100,7 +100,6 @@ public class SettingsView extends BorderPane implements Disposable {
             "gallery",
             "photo-detail",
             "ai",
-            "sync",
             "library",
             "recognition",
             "onboarding"

src/main/resources/messages.properties

@@ -142,7 +142,6 @@ settings.repairHashes.taskTitle=Repairing content hashes
 settings.help.tooltip=About / Credits
 settings.group.library=Library
 settings.group.ui=Appearance
-settings.group.sync=Synchronisation
 settings.group.thumbnails=Thumbnails
 settings.group.gallery=Gallery
 settings.group.photo-detail=Photo viewer
@@ -160,8 +159,6 @@ settings.ui.leftPanelWidth=Navigation drawer width
 settings.ui.rightPanelExpanded=Inspector panel expanded
 settings.ui.rightPanelWidth=Inspector drawer width
 settings.library.skipRemoveConfirmation=Skip the folder-removal confirmation
-settings.sync.enabled=Periodic background scan
-settings.sync.interval=Interval (minutes)
 settings.thumbnails.quality=Quality
 settings.thumbnails.ramCache=RAM cache (MB)
 settings.thumbnails.diskCache=Disk cache (MB)

src/main/resources/messages_fr.properties

@@ -145,7 +145,6 @@ settings.repairHashes.taskTitle=Réparation des hachages de contenu
 settings.help.tooltip=À propos / Crédits
 settings.group.library=Photothèque
 settings.group.ui=Apparence
-settings.group.sync=Synchronisation
 settings.group.thumbnails=Vignettes
 settings.group.gallery=Galerie
 settings.group.photo-detail=Visionneuse
@@ -163,8 +162,6 @@ settings.ui.leftPanelWidth=Largeur du tiroir de navigation
 settings.ui.rightPanelExpanded=Panneau inspecteur développé
 settings.ui.rightPanelWidth=Largeur du tiroir inspecteur
 settings.library.skipRemoveConfirmation=Ignorer la confirmation de retrait de dossier
-settings.sync.enabled=Analyse périodique en arrière-plan
-settings.sync.interval=Intervalle (minutes)
 settings.thumbnails.quality=Qualité
 settings.thumbnails.ramCache=Cache mémoire (Mo)
 settings.thumbnails.diskCache=Cache disque (Mo)

src/main/resources/preferences.yaml

@@ -91,18 +91,6 @@ ui:
     visible: false
     editable: false
 
-sync:
-  enabled:
-    type: BOOLEAN
-    label: settings.sync.enabled
-    default-value: true
-  interval-minutes:
-    type: INT
-    label: settings.sync.interval
-    default-value: 15
-    min: 1
-    max: 1440
-
 thumbnails:
   quality:
     type: STRING

src/test/java/org/icroco/pholio/infra/preferences/PreferenceServiceTest.java

@@ -492,7 +492,7 @@ class PreferenceServiceTest {
 
         SoftAssertions.assertSoftly(softly -> {
             softly.assertThat(preferences.visibleGroupNames())
-                  .containsExactly("library", "ui", "sync", "thumbnails", "gallery", "photo-detail", "ai", "imports", "recognition", "onboarding");
+                  .containsExactly("library", "ui", "thumbnails", "gallery", "photo-detail", "ai", "imports", "recognition", "onboarding");
             softly.assertThat(preferences.groupNames()).contains("window.main");
             softly.assertThat(preferences.getValue("ui", "color-mode", String.class)).isEqualTo("SYSTEM");
             softly.assertThat(preferences.getValue("ui", "theme-family", String.class)).isEqualTo("PRIMER");