build: ignore example + probe build artifacts

examples/snake/ leaves snake.s/.o/.combined.ww and the stripped
binary alongside its Makefile after a build; selfhost/test/
probes drop .combined.ww next to each .ww. None of these are
intended bootstrap inputs.

.gitignore

@@ -10,3 +10,14 @@
 # are intentionally tracked — they're frozen bootstrap inputs.
 selfhost/**/*.o
 selfhost/**/*.s
+
+# Test-probe leftovers. `ww build` drops .combined.ww next to the
+# source; the selfhost/test/ probes don't need them tracked.
+selfhost/test/*.combined.ww
+
+# examples/ build outputs. Each example has its own Makefile that
+# leaves the .s/.o/.combined.ww plus a stripped binary behind.
+examples/**/*.o
+examples/**/*.s
+examples/**/*.combined.ww
+examples/snake/snake