i18n: traduire les chaînes hardcodées restantes en anglais/français

- DateTime & Project : locale dayjs dynamique selon la langue active
- Images : bouton "Ajouter une ou plusieurs images" via t()
- ImagesEditPanel : placeholder, legend tags et bouton ajout via t()
- DynamicView : clé PHP "Autres pistes" traduite via t()
- Nouvelles clés : forms.selectTags, buttons.addSelectedImages, virtualSample.otherTracks

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/locales/en.json

@@ -70,7 +70,8 @@
     "loopAnimation": "Loop animation",
     "stopAnimation": "Stop animation",
     "compareTracks": "Compare tracks",
-    "exitCompare": "Exit compare mode"
+    "exitCompare": "Exit compare mode",
+    "addSelectedImages": "Add selected images"
   },
   "forms": {
     "email": "Email",
@@ -94,7 +95,8 @@
     "tags": "Tags",
     "selectVariation": "Select a variation",
     "uploadedFiles": "Uploaded files",
-    "addImages": "Add one or more images"
+    "addImages": "Add one or more images",
+    "selectTags": "Select one or more tags"
   },
   "auth": {
     "login": "Login",
@@ -184,7 +186,8 @@
     "dynamicPresentation": "Dynamic presentation",
     "staticView": "Static view",
     "noContent": "Content not available for this track",
-    "selectToCompare": "Select the track you want to compare"
+    "selectToCompare": "Select the track you want to compare",
+    "otherTracks": "Other tracks"
   },
   "errors": {
     "saveFailed": "Save failed",