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/parse.ludic

@@ -194,6 +194,8 @@ function p_postfix() -> Node {
       if e.a.kind == E_ID and e.a.s == "Motion" and e.s == "to" { g_uses_anim_rt = true }
       # Audio.* (#22) — any Audio method splices the audio runtime.
       if e.a.kind == E_ID and e.a.s == "Audio" { g_uses_audio = true }
+      # Http.* (#6) — any Http method splices the HTTP client runtime.
+      if e.a.kind == E_ID and e.a.s == "Http" { g_uses_http = true }
       # Tween.to/chain/delay/value/stop/parallel (#48): the fluent stateful handles
       # live in tween.ludic, advanced by an engine-owned system each Update tick.
       if e.a.kind == E_ID and e.a.s == "Tween" and (e.s == "to" or e.s == "chain" or e.s == "delay" or e.s == "value" or e.s == "stop" or e.s == "parallel") { g_uses_tween_rt = true }
@@ -429,6 +431,7 @@ var g_uses_input: bool = false    # a program used Input.bind/down/poll/… (act
 var g_uses_anim_rt: bool = false  # Anim.play/clip/on_frame/fired or Motion.to (#48) -> splice systems.ludic + force the reflection ABI
 var g_uses_tween_rt: bool = false # Tween.to/chain/delay/… (#48) -> splice tween.ludic + run esys_tween each Update
 var g_uses_audio: bool = false    # Audio.* (#22) -> splice audio.ludic; a windowed build also links audio.ll + AVFoundation
+var g_uses_http:  bool = false    # Http.* (#6) -> splice http.ludic; links http.ll + Foundation (macOS)
 
 function already_loaded(full: pointer) -> bool {
   var i = 0
@@ -657,6 +660,14 @@ function maybe_splice_runtime() -> void {
     do_import("runtime/native/audio.ludic")
     cur_dir = saved
   }
+  # Http.* (#6): splice the HTTP client. The transport (hs_* intrinsics) is native
+  # (linked from http.ll), but the response parser is pure Ludic; self-contained,
+  # so it works in a plain program too.
+  if g_uses_http {
+    cur_dir = ""
+    do_import("runtime/native/http.ludic")
+    cur_dir = saved
+  }
   # Anim.play/Motion.to sugar (#48): the writes live in systems.ludic and use the
   # reflection ABI, so splice it and force the world table even when the game does
   # not otherwise trip uses_engine_systems.