test: serialize local http unit tests

[ttbombadil]

Summary

• isolates unit tests that create real local HTTP listeners into a serial Vitest project
• keeps the remaining Node unit tests file-parallel
• prevents observed intermittent ECONNRESET / 30-second HTTP test timeouts under parallel file execution
• preserves the complete unit and coverage test set

Evidence

Before:

• isolated route tests stable
• combined affected route tests stable
• parallel unit-node intermittently failed in different local HTTP tests
• serial unit-node 1221/1221 PASS

After:

• serial HTTP project: 20/20 repeated runs PASS (109/109 each)
• full unit suite: 5/5 PASS (2113/2113 each)
• coverage: PASS
• security input tests: PASS (47/47)
• pre-push hook: PASS
• SonarQube Quality Gate: PASS

Scope

• no product changes
• only the 15 unit test files that open local HTTP listeners are serialized
• remaining unit-node tests remain parallel