[Tests] Register each test case with CTest instead of each test binary

Registering a test cost four edits across a dozen CMakeLists files: add_test,
add_executable, a conditional add_dependencies on gtest, and target_link_libraries.
The conditional branch was the trap -- it is only needed when GTest was fetched and
add_subdirectory'd, and omitting it yields undefined gtest symbols at link time --
so it was easy to leave out and impossible to notice until the link failed.

Fold all four steps into cockatrice_add_test() and migrate every test directory
onto it, with a cockatrice_add_manual_test() wrapper for the three benchmarks that
are built but deliberately kept out of ctest. The calls now read as a declaration
of what a test is rather than a transcript of how to register one.

While rewriting the registrations, replace add_test(NAME x COMMAND x) with
gtest_discover_tests(). Naming the binary as a single CTest entry meant a CI failure
reported only which binary failed, and ctest -R Suite.Case could not select an
individual case. Discovery raises the suite from 35 opaque entries to 469 real ones:
ctest -R ThemeMigrationTest.IsIdempotent now runs exactly that case, and
ctest -L server / -LE bench work off labels applied at registration.

Give every test a 60s TIMEOUT. CTest's implicit default is 1500s, so one hung
socket wait would stall CI for 25 minutes, and single_instance_manager_test already
does real QLocalSocket waits.

Dropping per-case granularity costs wall-clock time, since the suite becomes
process-spawn bound rather than CPU bound: serial ctest went from 3.8s to 30.8s. Run
it with -j in CI to recover it -- 7.6s at -j4, and 3.5s at -j8, both at or below
the old serial time. The binaries are parallel-safe: the only test claiming a fixed
resource scopes its local socket name to its own pid, so concurrent copies cannot
collide.

Also delete dummy_test, which asserted 1 == 1 and only proved the harness was
wired up -- something the other 468 cases already establish.

No test is added, removed, or changed by this commit; the 469 cases are the same
ones the 35 binaries contained.

.ci/compile.sh

@@ -306,7 +306,11 @@ fi
 
 if [[ $MAKE_TEST ]]; then
   echo "::group::Run tests"
-  ctest -C "$BUILDTYPE" --output-on-failure
+  # Every TEST() is its own CTest entry, so the suite is process-spawn bound rather than CPU
+  # bound and -j recovers nearly all of the per-process overhead. The test binaries are safe to
+  # run concurrently: the only one that claims a fixed resource is single_instance_manager_test,
+  # which already scopes its local socket name to its own pid so parallel copies cannot collide.
+  ctest -C "$BUILDTYPE" --output-on-failure -j "${CTEST_JOBS:-4}"
   echo "::endgroup::"
 fi