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/log_panel.hpp

@@ -0,0 +1,36 @@
+// Log window: shows the log lines the injected hook streams over the shared log
+// ring (see coop/log_ring.hpp). Pull new lines each frame from the IPC server,
+// keep a bounded rolling history, and render them with autoscroll + a filter.
+#pragma once
+
+#include <cstdint>
+#include <deque>
+#include <string>
+
+#include "coop/log_ring.hpp"
+
+namespace coop
+{
+
+class InjectionPanel;
+
+class LogPanel
+{
+public:
+	// Pull any new lines the hook emitted (call once per frame before draw()).
+	void pull(InjectionPanel& injection);
+
+	void draw();
+
+private:
+	void add_line(const LogRecord& rec);
+
+	std::deque<std::string> lines_;
+	char filter_[96] = {};
+	bool autoscroll_ = true;
+	std::uint64_t first_millis_ = 0; // hook clock at the first line, for relative timestamps
+
+	static constexpr std::size_t kMaxLines = 2000;
+};
+
+} // namespace coop