chore: migrate integration test helpers from process.env to vi.stubEnv

[enko]

Replace fragile process.env assignments and delete statements with
Vitest's vi.stubEnv() and vi.unstubAllEnvs() API across all four
integration test helper files. This ensures env variables are restored
atomically even if tests crash before afterAll runs, and brings all
helpers into consistency with health.test.ts (reference implementation).

Files migrated:

• auth.helpers.ts
• friends.helpers.ts
• search.helpers.ts
• postgis.helpers.ts

https://claude.ai/code/session_01SxmmhKAEjzLfZJv8GaFmCs

[github-actions]

🔍 Automated Code Review

Commit	`df02038`
Reviewed	2026-03-15T00:00:00Z
Status	✅ Approved

Findings

No issues found.

AGENTS.md Compliance

• ✅ Security requirements
• ✅ Architecture patterns
• ✅ Testing standards

Summary

Clean, focused refactoring that correctly migrates all four integration test helpers from manual process.env mutation and delete to Vitest's vi.stubEnv() / vi.unstubAllEnvs() API. This ensures atomic env cleanup even when tests crash before afterAll runs, and brings all helpers into consistency with the health.test.ts reference implementation. No logic changes — purely a test infrastructure improvement.

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_{🤖 Automated review by Claude Code • View CI Run}

[github-actions]

🎉 This PR is included in version 2.67.1 🎉

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