Tailscale UI does not scale after connecting a high DPI monitor

### What is the issue?

Tailscale UI is not properly scaled on a resolution change, when switched from a lower to a higher DPI after being started. Restarting the application helps, but this should be automatic.

### Steps to reproduce

Start Tailscale on, say, 1080p screen. Then connect a 4k screen as a primary monitor.

### Are there any recent changes that introduced the issue?

No

### OS

Windows 11 Pro

### OS version

24H2

### Tailscale version

1.84.2
tailscale commit: 5d271bebfc0d7f08e236290549d9a476550681b4
other commit: fb99774149da9383bf2a8747a163b1926762e9d7
go version: go1.24.2

### Bug report

BUG-abac6af1aa707a8ffa1b5c8016a95cb30a722b4afc9d1e4a62491bd94a5eea49-20250627134947Z-5d7ad267bc9f3159