Caddy: rewrite placeholder re-expansion, unbounded body buffer DoS, and fileHidden case-sensitivity bypass

Caddy v2.11.3 — Three vulnerabilities in handler/placeholder layer Tested against: caddy:2.11.3 official Docker image, SHA verified at runtime Reproduction environment: Docker Desktop 4.73.1 / Engine 29.4.3 on Windows 10 host, isolated containers, no network egress required for any of the exploit...