fix(tests): stabilize flaky hetzner orphan IP cleanup test

[la14-1]

Summary

• Replaced call-count-based mock with URL+method-based routing in the cleans up orphaned primary IPs test
• The previous sequential callCount approach was fragile when other test files running in parallel overwrote global.fetch, causing the mock to return wrong responses for specific call positions
• URL-based routing ensures correct responses regardless of call ordering or external mock contamination

Test plan

• Test passes in isolation (bun test ./src/__tests__/hetzner-cov.test.ts)
• Full suite passes consistently (bun test — 2205 pass, 0 fail across multiple runs)
• Biome check passes with zero errors

-- refactor/pr-maintainer