fix: defer import errors until the copy loop finishes

Errors and skips are collected while the copy loop runs and reported
once it ends. The final import state is exhaustive - success, already
added, invalid name, or nothing supported found - so every import run
reaches a terminal state and the pipeline notification always resolves
instead of lingering as an indeterminate progress bar.

app/src/main/res/values/strings.xml

@@ -66,8 +66,9 @@
     <string name="dictionary_management_title">Dictionaries</string>
     <string name="import_dictionary_button">Select files</string>
     <string name="import_error">Failed to import dictionary: %1$s</string>
-    <string name="import_file_exists">File already exists: %1$s</string>
+    <string name="import_file_exists">Dictionary already added: %1$s</string>
     <string name="import_invalid_file_name">Invalid file name: %1$s</string>
+    <string name="import_nothing_imported">No supported dictionary files were found in the selection</string>
     <string name="dictionary_source_url_hint">URL</string>
     <string name="dictionary_source_add_button">Add source</string>
     <string name="dictionary_source_duplicate">This URL already exists</string>