fix: ignore dateless sources when checking dictionary freshness

A source URL without the {DATE} placeholder is date-invariant, so its
HEAD probe always answers 200. Including such sources in the freshness
check made the checker report "server has a newer version" regardless
of the dated sources' state.

app/src/main/java/com/example/research/feature/download/repository/DictionaryChecker.kt

@@ -64,7 +64,14 @@ class DictionaryChecker(
             val previousDate = DateUtils.getPreviousDateString()
             val dictFiles = getDictFiles(folderUri, files)
 
-            val allHaveToday = enabledSources.all { source ->
+            val datedSources = enabledSources.filter { source ->
+                DictionarySource.hasDatePlaceholder(source.urlTemplate)
+            }
+            if (datedSources.isEmpty()) {
+                return@withContext true
+            }
+
+            val allHaveToday = datedSources.all { source ->
                 dictFiles.hasFileForSource(source, currentDate)
             }
 
@@ -72,19 +79,28 @@ class DictionaryChecker(
                 return@withContext true
             }
 
-            val allHaveYesterday = enabledSources.all { source ->
+            val allHaveYesterday = datedSources.all { source ->
                 dictFiles.hasFileForSource(source, previousDate)
             }
 
             if (allHaveYesterday) {
-                val serverHasToday = enabledSources.any { source ->
+                val serverHasToday = datedSources.any { source ->
                     isSourceAvailableOnServer(source, currentDate)
                 }
 
                 return@withContext !serverHasToday
             }
 
-            false
+            val serverCanOfferNewer = datedSources.any { source ->
+                when (probeSource(source, currentDate)) {
+                    SourceAvailability.AVAILABLE -> true
+                    SourceAvailability.NOT_FOUND ->
+                        probeSource(source, previousDate) == SourceAvailability.AVAILABLE
+                    SourceAvailability.UNKNOWN -> false
+                }
+            }
+
+            return@withContext !serverCanOfferNewer
         } catch (e: Exception) {
             Log.e(TAG, "Error checking currency: ${e.message}", e)
             false