Log window: stream the hook's logs over IPC into an in-app Log panel

Add a shared log ring (common/coop/log_ring.hpp): a lossy multi-producer /
single-consumer ring named coop_log_<pid>. The hook logs from several threads,
so producers claim a slot with fetch_add and publish each record with a
release store of its sequence; the consumer reads in order and tolerates
losing the oldest lines if it falls a whole ring behind.

The DLL's logf() now formats once and pushes every line to the ring (the file
trace stays as an opt-in mirror); the worker attaches the ring right after IPC
connect so bring-up is captured. The host (IpcServer) creates the ring at
injection time and exposes drain_logs(); a new LogPanel pulls new lines each
frame into a bounded rolling buffer and renders them with auto-scroll, a
filter, and clear. Added to the View menu (and UiState.show_log).

Verified against Phantom Brave via coop_audio_probe, which now also creates the
ring and drains it: the full hook bring-up trace streamed over IPC. All four
tests pass.

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

host/src/ipc/ipc_server.cpp

@@ -22,6 +22,15 @@ bool IpcServer::start(unsigned long target_pid)
 
 	block_ = block;
 	target_pid_ = target_pid;
+
+	// Log ring: the injected hook opens this and streams its log lines back for the
+	// Log window. Best-effort -- the rest of the tool works without it.
+	if (log_shm_.create(log_ring_name(target_pid), log_ring_total_size(kLogCapacity)))
+	{
+		log_ring_ = log_shm_.as<LogRing>();
+		log_ring_init(*log_ring_, kLogCapacity);
+		log_cursor_ = 0;
+	}
 	return true;
 }
 
@@ -96,6 +105,9 @@ void IpcServer::stop()
 		block_ = nullptr;
 	}
 	shm_.reset();
+	log_ring_ = nullptr;
+	log_shm_.reset();
+	log_cursor_ = 0;
 	target_pid_ = 0;
 }