fix(security): harden outbound client configuration in update checker and hub sync

[Wikid82]

Summary

Follow-up to #1492. Removes or contains the remaining production uses of a testing-only allowance in outbound clients:

• Update checker: the allowance is removed; the default client is always strict. Tests inject their own client.
• Hub sync: the allowance moves behind an unexported test-only seam.
• Uptime checks / LAPI registration: comments only, clarifying the intentional design (monitors may target local services).
• Removes unused LAPI health helpers and their tests (no non-test callers).

Behaviour note

A CrowdSec hub mirror configured via HUB_BASE_URL / HUB_MIRROR_BASE_URL can no longer point at a loopback address. Documented in docs/troubleshooting/crowdsec.md.

Testing

• Regression tests for the strict default clients and the test-only seam
• go test -race ./internal/services/... ./internal/crowdsec/..., go test ./internal/api/..., make lint-fast, pre-commit hooks pass
• Backend coverage 92.4%; patch coverage 100%
• QA report: docs/reports/qa_report.md

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Codecov Report

✅ All modified and coverable lines are covered by tests.

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✅ Supply Chain Verification Results

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📦 SBOM Summary

• Components: 1870

🔍 Vulnerability Scan

Severity	Count
🔴 Critical	0
🟠 High	0
🟡 Medium	0
🟢 Low	0
Total	0

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