Add cross timeline interaction gym

docs/gyms/cross-timeline-interactions/gym_pattern4_signal_chain.dtl

@@ -0,0 +1,33 @@
+# ============================================================
+# Pattern 4: Signal Event → GDScript → New Timeline
+# ============================================================
+# This timeline emits a signal. GDScript in gym_controller.gd
+# catches it and starts the target timeline.
+# ============================================================
+
+label start
+
+join Miko center
+
+Miko (neutral): This pattern uses a signal to bridge timelines.
+Miko (smile): I'm going to emit a signal, and GDScript will react.
+
+[wait time="1.0"]
+
+Miko (joy): Emitting signal: "demo_chain"!
+
+# This emits Dialogic.signal_event("demo_chain")
+# gym_controller.gd listens for this and starts
+# gym_pattern4_signal_target.dtl
+[signal arg=demo_chain]
+
+# This timeline continues until it ends...
+Miko (neutral): I'll keep going while the signal fires in the background.
+
+[wait time="0.5"]
+
+Miko (smile): ...and now I'm done here!
+
+# That's it. The signal handler in code started
+# gym_pattern4_signal_target.dtl which will take over.
+[end_timeline]