MCP: Nudge the the agent to use an explore agent for finding tables (#4147)

## Changes

Finding the right data set can consume a lot of tokens and we are
usually only interested in the final outcome. I've added a nudge to use
an `Explore Agent` when discovering tables.

<img width="1159" height="473" alt="Screenshot 2025-12-16 at 10 57 43"
src="https://github.com/user-attachments/assets/b810e9ca-68c6-42a6-8fee-ad61cbcfb007"
/>


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Author: fjakobs

experimental/apps-mcp/lib/prompts/flow.tmpl

@@ -54,3 +54,5 @@ Unity Catalog:
 
 Use separate arguments for catalog/schema: 'tables list samples tpcds_sf1' (not dot notation).
 Dot notation is only supported in `experimental apps-mcp tools discover-schema` and `experimental apps-mcp tools query`.
+
+It is STRONGLY RECOMMENDED to delegate the task of exploring catalogs, schemas, or tables in Unity Catalog to an Explore agent or a sub agent.