fix: speechmatics credential test ignored the configured region (#563)

The speechmatics branch of the /test route destructured only api_key out of the
decrypted credential, so testSpeechmaticsStt() passed realtimeUrl: undefined to
the sdk. ConnectionConfigFull only applies an override when the value is truthy,
so every credential was silently tested against wss://eu2.rt.speechmatics.com/v2
no matter which region was stored - a neu or wus key was judged by whatever eu2
happened to answer.

- pass speechmatics_stt_uri through from the route
- normalize it before handing it to the sdk. The field holds a bare hostname,
  which the sdk cannot use as-is: it appends the language, yielding
  "eu2.rt.speechmatics.com/en" and ERR_INVALID_URL. At call time the same value
  goes to mod_speechmatics_transcribe as SPEECHMATICS_HOST, which always
  connects over wss on port 443 with a path of /v2, so build exactly that url.
  Anything else - a full ws url, a port - now fails the test with an actionable
  message rather than passing against an endpoint only the test can reach, and a
  credential that has lost the field fails too: the feature server omits
  SPEECHMATICS_HOST when it is unset and the module refuses the session, so
  defaulting to a hosted region here would show a green check on a dead
  credential.
- record the speechmatics STT result with sttTestResult(), not ttsTestResult(),
  which is what every other STT vendor in this file does; the tts column was
  being stamped for an STT-only vendor

Adds coverage for the url building to the main test suite - it is the part of
this that can be exercised without an api key.

Co-authored-by: Claude Opus 5 (1M context) <noreply@anthropic.com>

lib/routes/api/speech-credentials.js

@@ -924,15 +924,15 @@ router.get('/:sid/test', async(req, res) => {
         }
       }
     } else if (cred.vendor === 'speechmatics') {
-      const {api_key} = credential;
+      const {api_key, speechmatics_stt_uri} = credential;
       if (cred.use_for_stt) {
         try {
-          await testSpeechmaticsStt(logger, {api_key});
+          await testSpeechmaticsStt(logger, {api_key, speechmatics_stt_uri});
           results.stt.status = 'ok';
-          SpeechCredential.ttsTestResult(sid, true);
+          SpeechCredential.sttTestResult(sid, true);
         } catch (err) {
           results.stt = {status: 'fail', reason: err.message};
-          SpeechCredential.ttsTestResult(sid, false);
+          SpeechCredential.sttTestResult(sid, false);
         }
       }
     } else if (cred.vendor === 'playht') {