Use the system spdlog, zlib and minizip.

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bb3478d..07f8962 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -71,7 +71,7 @@ endif()
 option(ENABLE_UI_QT "Build the UI (Qt)" ON)
 option(ENABLE_CLI "Build the CLI application" ON)
 
-add_subdirectory("${PROJECT_SOURCE_DIR}/lib/spdlog")
+find_package(spdlog REQUIRED)
 add_subdirectory("${PROJECT_SOURCE_DIR}/lib/mio")
 
 add_subdirectory(src)
diff --git a/src/main/CMakeLists.txt b/src/main/CMakeLists.txt
index 04fb741..c1e20ef 100644
--- a/src/main/CMakeLists.txt
+++ b/src/main/CMakeLists.txt
@@ -1,39 +1,10 @@
-# Add zlib and minizip dependencies
-# Prefer system zlib; otherwise build vendored static
-option(USE_SYSTEM_ZLIB "Use system-provided zlib if available" ON)
-
-if (USE_SYSTEM_ZLIB)
-  find_package(ZLIB QUIET)
-endif()
-
-if (NOT ZLIB_FOUND)
-  message(STATUS "System zlib not found; building vendored zlib (static)")
-  set(ZLIB_BUILD_TESTING OFF CACHE BOOL "[zlib] Enable Zlib Examples as tests"              FORCE)
-  set(ZLIB_BUILD_SHARED  OFF CACHE BOOL "[zlib] Enable building zlib shared library"        FORCE)
-  set(ZLIB_BUILD_STATIC  ON  CACHE BOOL "[zlib] Enable building zlib static library"        FORCE)
-  set(ZLIB_BUILD_MINIZIP OFF CACHE BOOL "[zlib] Enable building libminizip contrib library" FORCE)
-  set(ZLIB_INSTALL       OFF CACHE BOOL "[zlib] Enable installation of zlib"                FORCE)
-
-  add_subdirectory("${PROJECT_SOURCE_DIR}/lib/zlib"
-          "${CMAKE_BINARY_DIR}/lib/zlib"
-          EXCLUDE_FROM_ALL)
-
-  add_library(ZLIB::ZLIB ALIAS zlibstatic)
-endif()
-
-# Add minizip from our vendored zlib
-set(MINIZIP_DIR "${PROJECT_SOURCE_DIR}/lib/zlib/contrib/minizip")
-
-add_library(minizip STATIC
-        "${MINIZIP_DIR}/ioapi.c"
-        "${MINIZIP_DIR}/unzip.c"
-)
-if (WIN32)
-  target_sources(minizip PRIVATE "${MINIZIP_DIR}/iowin32.c")
-endif()
-
-target_include_directories(minizip PUBLIC "${MINIZIP_DIR}")
-target_link_libraries(minizip PUBLIC ZLIB::ZLIB)
+# Gentoo: use the system zlib and minizip.
+find_package(ZLIB REQUIRED)
+find_package(PkgConfig REQUIRED)
+pkg_check_modules(MINIZIP REQUIRED IMPORTED_TARGET minizip)
+add_library(minizip INTERFACE)
+target_include_directories(minizip INTERFACE "${MINIZIP_INCLUDEDIR}/minizip")
+target_link_libraries(minizip INTERFACE PkgConfig::MINIZIP)
 
 # Add libunarr
 message(INFO "Using built-in unarr")