Broadcast join wrongly chosen for un-analyzed tables, causing OOM

### Description

When a table (Olap or external: Hive/Iceberg/etc.) has not been analyzed, its row count is propagated as `UNKNOWN_ROW_COUNT` (-1). `StatsCalculator` clamps this to 1 row so the cost model can keep working, but `JoinUtils.checkBroadcastJoinStats` then sees "1 row" and picks the table as the broadcast join build side. For a large un-analyzed table this materializes the full table on every BE node and OOMs.

### Steps to reproduce

1. Create a large table and do **not** run `ANALYZE`.
2. Join it against another table with a session that allows broadcast joins.
3. Observe the planner picks a broadcast join; runtime OOMs.

### Expected behavior

The optimizer should refuse broadcast when the build-side row count was clamped from unknown, falling back to a shuffle join.

### Actual behavior

Broadcast join is chosen, leading to OOM.

Start by tracing how StatsCalculator represents UNKNOWN_ROW_COUNT and how JoinUtils.checkBroadcastJoinStats consumes the clamped value. Reproduce with a large unanalyzed table joined under a session that allows broadcast joins, then verify the planner refuses broadcast and selects a shuffle join without causing runtime OOM.

Written by the indexing model from the issue text.