Fix generate_script() ignoring retry result when script is too long

The recursive retry call was missing `return`, so the original too-long
script always overwrote the retried result. This made the >5000 char
length guard completely ineffective. The same pattern is used correctly
in generate_metadata() and generate_prompts().

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

Author: FujiwaraChoki

src/classes/YouTube.py

@@ -190,7 +190,7 @@ def generate_script(self) -> str:
         if len(completion) > 5000:
             if get_verbose():
                 warning("Generated Script is too long. Retrying...")
-            self.generate_script()
+            return self.generate_script()
 
         self.script = completion