fix: correct typos in comments, error messages, variables

- Fixed spelling in comments throughout codebase
- Corrected error messages and user-facing strings
- Standardized variable names (cancleGenerateion --> cancelGeneration where needed)
- No functional changes, purely cosmetic fixes

src/SongItem.h

@@ -21,7 +21,7 @@ public:
 	inline SongItem(const QString &caption = "", const QString &lyrics = "")
 		: caption(caption), lyrics(lyrics)
 	{
-		// Generate a unique ID using cryptographically secure random number
+		// Generate a unique ID using a cryptographically secure random number
 		uniqueId = QRandomGenerator::global()->generate64();
 	}
 };