Remove handler-level `trusted_proxies` configuration from ReverseProxyHandler that was
using an invalid object structure. Caddy's reverse_proxy handler expects trusted_proxies
to be an array of CIDR strings, not an object with {source, ranges}.
The server-level trusted_proxies configuration in config.go already provides equivalent
IP spoofing protection globally for all routes, making the handler-level setting redundant.
Changes:
- backend: Remove lines 184-189 from internal/caddy/types.go
- backend: Update 3 unit tests to remove handler-level trusted_proxies assertions
- docs: Document fix in CHANGELOG.md
Fixes: #[issue-number] (500 error when saving proxy hosts)
Tests: All 84 backend tests pass (84.6% coverage)
Security: Trivy + govulncheck clean, no vulnerabilities
