feat(launcher): Process.*, Http.save_to/received/expected, App.window_hide/show

Process.spawn/poll/kill/free - non-blocking child processes with no shell: posix_spawn on
macOS (process.ll), CreateProcessW with MSVC-quoted arguments and no console window on
Windows (process_win.ll), linked only when a program uses Process.*.

Http.save_to streams a response body into a file (NSURLSession with a run-time delegate
class on macOS, the WinHTTP read loop on Windows); Http.received / Http.expected report
progress while it is pending. Freeing a pending request cancels it and parks the slot
until the worker has finished.

App.window_hide / App.window_show take the game's window off the screen and back without
closing it; the run goes on while hidden. Docs, examples, tests and a changeset.

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

docs/language/http/_section.md

@@ -4,6 +4,6 @@ title: Http
 order: 8
 ---
 
-A poll-based HTTP / HTTPS client for out-of-band data — leaderboards, cloud saves, remote config, telemetry, downloads. Open a request with <a href="http-get.html"><code>Http.get</code></a> / <a href="http-post.html"><code>Http.post</code></a> (or <a href="http-open.html"><code>Http.open</code></a> to add headers first), then each frame call <a href="http-poll.html"><code>Http.poll</code></a> — it returns <code>-1</code> while pending, <code>0</code> on error, or the status code — so the frame never blocks. Read the reply with <a href="http-status.html"><code>Http.status</code></a> / <a href="http-ok.html"><code>ok</code></a> / <a href="http-text.html"><code>text</code></a> / <a href="http-header.html"><code>header</code></a>, and pair it with <code>Json.*</code> for (de)serialization. TLS is the system's, on by default.
+A poll-based HTTP / HTTPS client for out-of-band data — leaderboards, cloud saves, remote config, telemetry, downloads. Open a request with <a href="http-get.html"><code>Http.get</code></a> / <a href="http-post.html"><code>Http.post</code></a> (or <a href="http-open.html"><code>Http.open</code></a> to add headers first), then each frame call <a href="http-poll.html"><code>Http.poll</code></a> — it returns <code>-1</code> while pending, <code>0</code> on error, or the status code — so the frame never blocks. Read the reply with <a href="http-status.html"><code>Http.status</code></a> / <a href="http-ok.html"><code>ok</code></a> / <a href="http-text.html"><code>text</code></a> / <a href="http-header.html"><code>header</code></a>, and pair it with <code>Json.*</code> for (de)serialization. TLS is the system's, on by default. A large download goes to a file instead of memory with <a href="http-save_to.html"><code>Http.save_to</code></a>, and <a href="http-received.html"><code>Http.received</code></a> / <a href="http-expected.html"><code>expected</code></a> drive a progress bar while it is pending.
 
-HTTP depends on the network and the wall clock, so — like <code>Net.*</code> and <code>Time.now</code> — it is <strong>out-of-band</strong> and must never feed the deterministic lockstep/replay simulation. The transport is macOS-only for now; the raw-response parser (<a href="http-parse.html"><code>Http.parse</code></a>) is pure and portable.
+HTTP depends on the network and the wall clock, so — like <code>Net.*</code> and <code>Time.now</code> — it is <strong>out-of-band</strong> and must never feed the deterministic lockstep/replay simulation. The transport is NSURLConnection / NSURLSession on macOS and WinHTTP on Windows; the raw-response parser (<a href="http-parse.html"><code>Http.parse</code></a>) is pure and portable.