CVE-2026-55677: Echo: Encoded slash (%2F) bypasses route-level protection and exposes static files

Echo’s router and static file handler disagree on URL path decoding. The router matches routes using the raw encoded path (preserving %2F as-is), while StaticDirectoryHandler unescapes %2F to / before resolving filesystem paths. This allows an attacker to bypass route-level access controls and read static files without authorization.