docs(examples): drop the stale ssrf address-header workaround

[rennf93]

Closes #81

Removes the logSensitiveHeaders address-header workaround from examples/simple_app/index.php and examples/advanced_app/src/config.php, rewrites the address-header note in examples/simple_app/README.md, and drops the stale "delegated to logSensitiveHeaders" clause from the "Known surface gaps" line in AGENTS.md. The engine skips ssrf for the proxy identity headers by default and has excludedDetectionHeaders and excludedSemanticDetectionHeaders, so the examples need no opt-out. docs/configuration.md already describes the real surface.

The workaround was worse than the default: it skipped those headers from detection entirely. I ran both examples with php -S against Redis, before (origin/master) and after, with the same requests as the live smoke job plus forwarded-header cases. Before: X-Forwarded-For: <script>alert(1)</script> returned 200 (simple_app) and X-Forwarded-Host: <script>alert(1)</script> returned 200 (advanced_app). After: both return 400, while Host: localhost, X-Forwarded-For: 203.0.113.9, 10.0.0.1 and X-Real-IP still return 200, the XSS query still returns 400, the bad user agent still returns 403, and the admin routes behave as before.

Local gate: make lint and make test (36 passed, 0 failed) with Redis on 127.0.0.1. Only examples and docs changed, no src/.