Add HealthCheck middleware

[setlin-hacktron]

Recreates deb-hacktron#25 in this fork to reproduce outside-diff findings in a Hacktron app scan (WEB-744 testing).

Same base commit and diff as the original (base/pr-620 ← healthcheck-middleware), so the scan should surface the same in-diff and outside-diff findings here.

[hacktron-app-stg]

3 issues found across 3 files

Severity	Count
	1
	1
	1

Findings outside your changes (3)

3 additional security findings were found outside your changes. Details are hidden on public repositories — review them in Hacktron: finding 1 · finding 2 · finding 3

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[setlin-hacktron]

@HacktronAI review

[setlin-hacktron]

@HacktronAI review

[setlin-hacktron]

@HacktronAI review

[hacktron-app-stg]

Hacktron Security Check - Skipped

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