fix: handle misheard filler words in base enhancement prompt

- Add detection for unnatural conjunctions/articles that may be misheard fillers
- Ensures base prompt catches cases where Whisper misrecognizes "um" as "and" etc
- Provides solid foundation for all enhancement presets (Email, Prompts, Commit)

This addresses acoustic confusion where filler sounds are mistranscribed as
real words at the neural network level before normalization can catch them.

Author: moinulmoin

src-tauri/src/ai/prompts.rs

@@ -76,6 +76,7 @@ pub fn build_enhancement_prompt(
 const DEFAULT_PROMPT: &str = r#"THEN clean up this voice transcription:
 
 - Remove filler words (um, uh, like) and stutters
+- Fix unnatural conjunctions or articles that seem out of place
 - Fix grammar, spelling, and common homophones  
 - Correct technical terms and programming terminology
 - Format numbers, dates, times naturally