Restructure bin/: deployables at root, tests and tools in subfolders

Only the shipping artifacts (coop_host.exe, coop_hook.dll, coop_hook_x86.dll,
coop_inject_x86.exe, steam_api64.dll, steam_input_actions.vdf) now land in the
bin/<config>/ root, so it can be copied wholesale into a donor game folder. Test
exes (plus the coop_tone fixture) build into bin/<config>/tests/ and the dev probes
into bin/<config>/tools/, via a new coop_output_subdir() CMake helper.

The probes resolve coop_hook.dll / the x86 injector from the deployable root one
level up (new common/coop/tool_paths.hpp: deployed_artifact_path checks next-to-exe
then parent). coop_tone is co-located with the tests so audio_loopback_test's
"spawn coop_tone.exe next to me" lookup is unchanged.

Verified from a clean bin/: root holds only deployables; ctest x64 7/7 and x86 3/3
green (incl. audio_loopback_test driving coop_tone from tests/).

Also convert the roadmap Planned list to bullets and drop this (now-done) item.

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

common/include/coop/tool_paths.hpp

@@ -0,0 +1,52 @@
+// Resolve artifacts that ship in the deployable bin/<config>/ root even when the
+// running executable lives in a sibling subfolder (e.g. dev tools staged under
+// bin/<config>/tools/). The probes use this to find coop_hook.dll and the x86
+// injector helper, which stay at the root while the probes themselves do not.
+#pragma once
+
+#include <cstddef>
+#include <string>
+
+#include <windows.h>
+
+namespace coop
+{
+
+// Directory of the current executable, with a trailing separator.
+inline std::wstring exe_directory()
+{
+	wchar_t buf[MAX_PATH] = {};
+	GetModuleFileNameW(nullptr, buf, MAX_PATH);
+	std::wstring path(buf);
+	const std::size_t slash = path.find_last_of(L"\\/");
+	return slash == std::wstring::npos ? std::wstring() : path.substr(0, slash + 1);
+}
+
+// Full path to a deployed artifact `name`: prefer one next to the running exe, else
+// one directory up (the deployable root, when the exe runs from a tools/ subfolder).
+// Falls back to the next-to-exe path so callers can report a sensible "not found".
+inline std::wstring deployed_artifact_path(const wchar_t* name)
+{
+	const std::wstring here = exe_directory() + name;
+	if (GetFileAttributesW(here.c_str()) != INVALID_FILE_ATTRIBUTES)
+	{
+		return here;
+	}
+	std::wstring dir = exe_directory();
+	if (!dir.empty())
+	{
+		dir.pop_back(); // drop the trailing separator before going up a level
+	}
+	const std::size_t slash = dir.find_last_of(L"\\/");
+	if (slash != std::wstring::npos)
+	{
+		const std::wstring up = dir.substr(0, slash + 1) + name;
+		if (GetFileAttributesW(up.c_str()) != INVALID_FILE_ATTRIBUTES)
+		{
+			return up;
+		}
+	}
+	return here;
+}
+
+} // namespace coop