Add HTTPRequest/HTTPResponse: real HTTP parsing on the Parser/StreamReader stack

Stage 2 of the APIServer plan. This codebase has only ever sat behind a
CGI gateway - IMFRequest/IMFResponse/IMFMessage predate the
StreamReader/Parser rebuild and are stubs (IMFResponse's header-emission
calls addHeader()/output(), neither of which exist on the class;
IMFRequest is a fragile non-resumable 3-token line split). Nothing in
this repo has ever actually parsed a raw HTTP request off a socket.

HTTPRequest : public Parser fills that gap the same way every other
Parser here is built: REQUEST_LINE -> HEADERS -> BODY -> DONE, chaining
LineParser (request line) and IMFHeader (headers, reused as-is - HTTP
header syntax is IMF-derived, nothing email-specific in IMFHeader
itself) via checkParse() over one shared StreamReader, exactly the
pattern CGIFormData already established for chaining IMFHeader/
IMFBoundary. The BODY state dispatches on Content-Type as CGIFormData
itself does for CGI bodies - application/x-www-form-urlencoded and
multipart/form-data delegate directly to CGIFormData (reused, not
reimplemented), anything else is captured as a raw body (e.g. JSON).
Query string is split off the path before anything else sees it.
getHeader() does a case-insensitive lookup (HTTP header names are
case-insensitive per RFC 7230, unlike IMFHeader's own std::map, which
compares byte-for-byte) since a route handler constantly needs this and
getting it wrong would be a silent framing bug, not a cosmetic one.

The boundary-extraction code mirrors __jet.cpp's own fix exactly (same
cursor-mutation trap: ZString::find() leaves the searched string's
cursor at the match, and CGIFormData's constructor copy-constructs its
own contentType member from whatever's passed in, inheriting that same
moved cursor unless reset() first - would otherwise silently miss its
own startsWith() dispatch checks).

HTTPResponse is a small, new, output-only builder (status line + a real
headers container + body, Content-Length auto-computed unless set
explicitly) - deliberately not patched from IMFResponse, which has
nothing safe to extend.

v1 limitations, flagged not fixed (matching the standard already set by
other Parser subclasses here for known-but-out-of-scope gaps): chunked
Transfer-Encoding isn't supported, and repeated header names last-wins
(inherited from IMFHeader's own std::map).

Verified live via testing/http_test.cpp (34 assertions, new - now wired
into testing/compile): byte-at-a-time GET with a query string and
case-insensitive header lookup; a GET with no query string; a POST with
an urlencoded body deliberately split mid-body (not just mid-header)
across two feed() calls, confirming the CGIFormData delegation resumes
correctly; a raw JSON POST body; testing/http_request.data (a real
fixture, previously unused - normalized from its stored LF line endings
to real CRLF, since HTTP requires CRLF and IMFHeader enforces that
strictly) fed byte-at-a-time; and HTTPResponse::serialize() both with an
auto-computed and an explicitly-set Content-Length (no duplicate
header). Also reran the full existing testing/compile suite
(zstring/mstring/jstring/mfile/jfile) against the rebuilt libCoreUtils.a
to confirm no regression from the two new files.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

HTTPResponse.cpp

@@ -0,0 +1,53 @@
+#include "HTTPResponse.h"
+#include <strings.h>
+
+namespace coreutils {
+
+   HTTPResponse::HTTPResponse() {
+      statusText = "OK";
+   }
+
+   void HTTPResponse::setStatus(int code, ZString text) {
+      statusCode = code;
+      statusText = text;
+   }
+
+   void HTTPResponse::setHeader(ZString name, ZString value) {
+      headers[MString(name)] = MString(value);
+   }
+
+   void HTTPResponse::setBody(ZString bodyIn) {
+      body = bodyIn;
+   }
+
+   MString HTTPResponse::serialize() {
+      bool hasContentLength = false;
+      for (auto &pair : headers) {
+         MString key = pair.first;
+         if (strcasecmp(key.c_str(), "Content-Length") == 0)
+            hasContentLength = true;
+      }
+
+      MString out;
+      out << "HTTP/1.1 ";
+      out << MString(std::to_string(statusCode));
+      out << " ";
+      out << statusText;
+      out << "\r\n";
+      for (auto &pair : headers) {
+         out << pair.first;
+         out << ": ";
+         out << pair.second;
+         out << "\r\n";
+      }
+      if (!hasContentLength) {
+         out << "Content-Length: ";
+         out << MString(std::to_string(body.getLength()));
+         out << "\r\n";
+      }
+      out << "\r\n";
+      out << body;
+      return out;
+   }
+
+}