Make auto the default speech language and carry what was detected through

New installs start detecting instead of being locked to one language; a stored
value from before this default still wins. The dictation chain asks
transcribe_detected() in auto mode, records the detected code in history as
speech_language, hands it to the cleanup prompt (a detected Turkish recording
gets the Turkish prompt and glossary rule), and reports it on the socket reply.
The stale comment claiming whisper.cpp's -l auto does not detect is corrected.

tests/test_config.py

@@ -259,6 +259,16 @@ class CleanupPrompt(DikteTest):
     def test_no_glossary_means_no_rule_about_one(self):
         self.assertEqual(cfg.Config().cleanup_prompt(), cfg.CLEANUP_PROMPT_EN)
 
+    def test_a_detected_turkish_recording_gets_the_turkish_prompt(self):
+        """Auto mode learns what was heard, and that decides the prompt rather
+        than the interface language."""
+        self.write_config({"ui_language": "en", "transcribe_prompt": "Paraşüt"})
+        conf = cfg.Config()
+        self.assertIn("KONUŞMACININ KULLANDIĞI İSİM VE TERİMLER",
+                      conf.cleanup_prompt(speech="tr"))
+        self.assertIn("NAMES AND TERMS THE SPEAKER USES",
+                      conf.cleanup_prompt(speech="de"))
+
     def test_subtitles_use_their_own_prompt(self):
         conf = cfg.Config()
         self.assertNotEqual(conf.cleanup_prompt(subtitles=True), conf.cleanup_prompt())