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/ui/app_chrome.cpp

@@ -24,6 +24,7 @@ float draw_main_menu_bar(UiState& ui, const FrameStats& stats)
 		ImGui::MenuItem("Injection", nullptr, &ui.show_injection);
 		ImGui::MenuItem("Video mirror", nullptr, &ui.show_video);
 		ImGui::MenuItem("Audio mirror", nullptr, &ui.show_audio);
+		ImGui::MenuItem("Log", nullptr, &ui.show_log);
 		ImGui::Separator();
 		ImGui::MenuItem("Debug details", nullptr, &ui.debug_details);
 		ImGui::EndMenu();