X enhancement: highlight start/middle/end segment of BTC address for visual verification

### Problem
Clipboard malware can replace the full BTC address, and users often verify only the beginning and end of the address.

### Suggestion
Highlight not only the start and end, but also a small segment of the middle of the BTC address to improve visual verification.

### Why this helps
- Improves human visual verification
- No protocol changes
- No privacy impact
- Low implementation cost

### Context
Observed in real user support cases when moving BTC from hardware wallets to software wallets.