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>

host/CMakeLists.txt

@@ -76,6 +76,8 @@ if(EXISTS "${COOP_STEAM_SDK_DIR}/public/steam/steam_api.h")
 		coop_common
 		xinput
 		"${COOP_STEAM_SDK_DIR}/redistributable_bin/win64/steam_api64.lib")
+	# Dev tool -> bin/<config>/tools/ (its steam_api64.dll copy follows via TARGET_FILE_DIR).
+	coop_output_subdir(tools coop_steam_input_probe)
 	add_custom_command(TARGET coop_steam_input_probe POST_BUILD
 		COMMAND ${CMAKE_COMMAND} -E copy_if_different
 			"${COOP_STEAM_SDK_DIR}/redistributable_bin/win64/steam_api64.dll"