Relax response-body gating so HTML and XHTML can be buffered when
Transfer-Encoding is chunked-only, or when Content-Length is missing,
while still rejecting non-identity encodings that are not chunked HTML
and other non-HTML cases.
Update modifyHTML to cap reads for unknown length, splice the original
stream back when the cap is hit, and document the behavior in the
package README. Extend tests for themed middleware and the rewrite gate.
Added details on request-variable substitution, explaining how it
reads fields from the active outbound request and resolves upstream
variables from the current route context.
Refactor response body modification to only allow text-like content types
(JSON, YAML, XML, etc.) instead of all HTML responses.
Body modification is now
blocked for binary content and transfer/content encoded responses, while status
code and headers can still be modified.
This prevents issues with compressed or streaming responses while
maintaining the ability to modify text-based API responses.
