#346 Disable AQE in broadcast notebook

[jathavaan]

Summary

• Disable Adaptive Query Execution (AQE) around the timed spatial join in the broadcast notebook
• AQE was rewriting Sedona's BroadcastIndexJoinExec into Spark's native BroadcastNestedLoopJoinExec (brute-force cross product), causing spark.driver.maxResultSize overflow at national scale
• Mirrors the same AQE guard already present in the partitioned notebook

Closes #346

Test plan

• Run broadcast notebook on Databricks at national scale and verify join completes without maxResultSize error
• Confirm Sedona selects BroadcastIndexJoin (check Spark UI physical plan)

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