Agentic lakehouse: specialized sub-agents for optimization and analysis

### Task Description

**What needs to be done:**
Sub-agents the main agent can delegate to: table optimization (layout, compaction/clustering tuning, eventually closed-loop), deep data analysis, and table/timeline visualization.

**Why this task is needed:**
Separate focused agents with narrower toolsets outperform one generalist as capabilities grow.

### Task Type
Other

### Related Issues
**Parent feature issue:** #19256