Add tutorial READMEs and fix tutorial return codes

Add README.md files for moeo/tutorial/Lesson{1-4}, smp/tutorial/Lesson{1-4},
and mo/tutorial/Lesson9 — these tutorials had no documentation.

Fix return 1 → return 0 in 28 tutorial main() functions across mo/ and
smp/ that unconditionally returned failure status.

smp/tutorial/Lesson4/README.md

@@ -0,0 +1,31 @@
+# Dynamic island topology
+
+Three islands start with a ring topology and switch to a complete topology
+after 10 seconds of computation.
+
+Same QAP problem as Lessons 1-2.
+
+## Running
+
+From the `build/smp/tutorial/Lesson4` directory:
+
+```shell
+./lesson4_topology
+```
+
+## How it works
+
+A callback function registered with the islands triggers the topology
+change:
+
+```c++
+void changeTopo(IslandModel<Indi>* _model, AbstractTopology& _topo)
+{
+    // ... after 10 seconds:
+    _model->setTopology(_topo);
+}
+```
+
+The topology can be changed at runtime via `model.setTopology()`, so you
+can implement adaptive communication patterns based on time, convergence,
+or any other criterion.