schema_index times out on large Snowflake databases

## Bug

`schema_index` times out when indexing a Snowflake database with a large number of schemas/tables, with no progress feedback or ability to scope the operation.

## Steps to Reproduce

1. Connect to a Snowflake warehouse with many schemas/tables
2. Run `schema_index [warehouse=jaffle_shop]`
3. Indexer times out with no useful output

## Expected Behavior

- **Progress feedback**: Show incremental progress (e.g., "Indexed 5/42 schemas...")
- **Timeout configuration**: Allow users to increase the timeout for large databases
- **Partial results**: Return whatever was indexed before the timeout rather than failing entirely
- **Scoping**: Allow indexing a specific schema rather than the entire database (e.g., `schema_index [warehouse=jaffle_shop, schema=public]`)

## Context

Large production Snowflake databases can have hundreds of schemas and thousands of tables. The current indexer appears to attempt a full catalog scan with a fixed timeout, making it unusable for these environments.