Add cross timeline interaction gym

docs/gyms/cross-timeline-interactions/gym_pattern2_caller.dtl

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+# ============================================================
+# Pattern 2: Jump + Return (Subroutine Pattern)
+# ============================================================
+# This timeline CALLS a sub-timeline (gym_pattern2_subroutine.dtl)
+# which does some work, then RETURNS control back here.
+# ============================================================
+
+label start
+
+join Miko center
+join Advisor right
+
+Miko (neutral): I'm in the caller timeline.
+Advisor (pl5): Let me check something in the subroutine...
+
+# Save current position and jump to the subroutine
+jump gym_pattern2_subroutine/start
+
+# Execution resumes HERE after the subroutine calls "return"
+label after_return
+
+Miko (joy): Welcome back! The subroutine finished.
+Advisor (pl5): Notice how we resumed right where we left off.
+
+[wait time="1.0"]
+
+# Let's demonstrate: the subroutine set a variable
+if {Gym.sub_value} == 42:
+    Miko (smile): The subroutine set `Gym.sub_value` to {Gym.sub_value}!
+    Advisor (pl5): Variables set in subroutines persist after return.
+else:
+    Miko (doubt): Hmm, the subroutine didn't set the value correctly.
+    Advisor (doubt): Something went wrong — `Gym.sub_value` is {Gym.sub_value}.
+
+[wait time="1.5"]
+
+Miko (neutral): That's the subroutine pattern in a nutshell!
+Advisor (pl5): Jump → work → return. Powerful for reusable dialog chunks.
+
+[wait time="1.0"]
+
+jump gym_main/menu