feat(http): Http.* poll-based HTTP/HTTPS client over a native NSURLConnection backend (#6)

Adds the Http.* namespace and its transport, the HTTP client from #6. The JSON
companion the proposal called for already shipped as Json.* (#44).

- runtime/native/http.ll: the macOS transport — NSURLConnection driven through
  the objc runtime C ABI (no ObjC/C source), run on a detached pthread so the
  frame never blocks; TLS is the system's, on by default. A fixed slot pool holds
  each in-flight request; the worker publishes status/body/response behind an
  atomic done flag (release/acquire). Spliced + Foundation linked only when a
  program uses Http.*.
- runtime/native/http.ludic: the Http.* runtime — get/post/request, the
  open/set/body/send builder, poll/status/ok/text/body_len/header/free, plus a
  pure-Ludic response parser (Http.parse + case-insensitive header lookup) that
  is transport-independent and portable.
- compiler: Http.* dispatch, g_uses_http splice, hs_* transport intrinsics +
  declarations, the conditional Foundation link, and a new \r string/char escape
  the protocol needs.
- docs: a full docs/language/http section (16 pages); check-impl/check-docs green.
- test: examples/library/http.ludic self-asserts the parser offline (Darwin-gated
  build via the canonical path, since it links Foundation).

Verified end to end against real endpoints: HTTPS GET (200 + headers + body) and
POST (body + custom header). HTTP is out-of-band and never feeds the
deterministic sim. Reseeded; suites green (81 + 29).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/frontend/lex.ludic

@@ -60,6 +60,7 @@ function lex(src: pointer) -> void {
           let e = src[i + 1]
           var r = e
           if e == 110 { r = 10 }
+          if e == 114 { r = 13 }
           if e == 116 { r = 9 }
           if e == 48  { r = 0 }
           out[j] = r;  j = j + 1;  i = i + 2
@@ -86,6 +87,7 @@ function lex(src: pointer) -> void {
       if src[i] == 92 {
         let e = src[i + 1]
         if e == 110 { v = 10 }
+        if e == 114 { v = 13 }
         if e == 116 { v = 9 }
         if e == 48  { v = 0 }
         i = i + 2