Always run language detection even with single language configured (#26)

Always run language detection even with single language configured (#26)

Previously, language detection was skipped when only one language was
configured, returning the configured language directly. This made it
impossible to detect misconfiguration (e.g., only EN configured but
receiving DE text).

Now language detection always runs, providing:
- Actual detected language in logs (detectedLanguage field)
- Confidence score for debugging
- usedFallback=true when detected language isn't configured

Performance impact is negligible (~0.01-0.05ms per detection).