fix tag search case sensitivity

_filterNotes lowercases the query so searchTags contains e.g. '#work',
but _extractTags preserves original case from file content ('#Work').
The startsWith comparison was case-sensitive, causing all tag searches
to fail whenever the file used any uppercase in tag names.

Fix: toLowerCase() on the noteTag side before comparing.

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

lib/note_list.dart

@@ -335,9 +335,9 @@ Happy note taking! ✨
         // ✅ Read file content ONLY if `Include File Content` is enabled
         final content = _includeFileContent ? note.readAsStringSync().toLowerCase() : '';
 
-        // ✅ Match partial tags instead of requiring full matches
+        // ✅ Match partial tags instead of requiring full matches (case-insensitive)
         final matchesTags = searchTags.every((tag) =>
-            noteTags.any((noteTag) => noteTag.startsWith(tag)));
+            noteTags.any((noteTag) => noteTag.toLowerCase().startsWith(tag)));
 
         if (!_includeFileContent) {
           return relativePath.contains(normalizedSearch) && matchesTags;