McpExtension built its middleware chain entirely internally, so a consumer had no
way to add rate limiting, audit logging or tracing to /mcp — routine on every other
Flash route. McpConfig.middleware(...) appends to the chain after the transport
guards and after whatever McpSecurity resolved to, so it composes with OAuth2
protection instead of replacing it, and never satisfies REQUIRED.
Docs: flash-ext-auth-core and flash-ext-auth-oidc both get a docs/ directory —
oidc had none at all, and its module README documented types that no longer exist.
Includes a migration table from flash-ext-oidc.
