Fix/cmake test only build (#6709)

* fix(cmake): guard filter_string_test behind WITH_ORACLE or WITH_CLIENT. filter_string_test links against libcockatrice_filters, which is only built when WITH_ORACLE or WITH_CLIENT is enabled. Without this guard, test-only builds fail at configure time because the target doesn't exist. The guard condition mirrors the one in the root CMakeLists.txt that controls whether libcockatrice_filters is built.

* fix(cmake): centralize TEST_QT_MODULES in FindQtRuntime.cmake  Each test CMakeLists.txt was independently defining TEST_QT_MODULES with its own subset of Qt modules. This duplicated knowledge that already lives in FindQtRuntime.cmake (which handles module discovery for all other targets: SERVATRICE, COCKATRICE, ORACLE). Consolidate into a single definition using the union of all test requirements (Concurrent Network Svg Widgets), matching the existing pattern for application-target modules. This ensures test-only builds (-DTEST=ON without application targets) discover all necessary Qt components.

* fix(cmake): guard libcockatrice_network behind application targets. libcockatrice_network is only needed by the client, server, and oracle targets. Other application-specific libraries (settings, models, filters) already have similar guards. This was an oversight that caused test-only builds to fail when network dependencies weren't available.

tests/CMakeLists.txt

@@ -1,3 +1,5 @@
+# NOTE: Qt modules for tests are defined centrally in cmake/FindQtRuntime.cmake (the _TEST_NEEDED variable).
+# If a new test needs additional Qt modules, add them there — not in individual test CMakeLists.txt files.
 enable_testing()
 
 add_test(NAME dummy_test COMMAND dummy_test)