Allow manually-added servers to be linked to Hetzner Cloud instances by
matching IP address. Once linked, servers gain power controls and status
monitoring.
Changes:
- Add getServers() and findServerByIp() methods to HetznerService
- Add Hetzner linking UI section to Server General page
- Add unit tests for new HetznerService methods
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
