Surface debug logs when adding log-level devug.

## Problem
When `confluent_sql.connect()` fails, users see only:

```
Runtime Error
Error running SQL 'select 1 as id': confluent_sql connection error
```

And no more detailed information shows if changing the debug level at the dbt adapter level.

## Example from a real incident

A user installed `dbt-confluent==0.1.0` from PyPI and saw:

```
Runtime Error
Error running SQL 'select 1 as id': confluent_sql connection error
```

The actual chained (but hidden) exception was:

```
TypeError: connect() got an unexpected keyword argument 'environment'

"confluent_sql connection error" isn't actionable. "TypeError: got an unexpected keyword argument 'environment'" immediately points to a version mismatch. This pattern generalizes: auth failures surface as
`httpx.HTTPStatusError 401`, wrong regions as DNS errors, etc. — all currently invisible in default output
```

## Desired behavior

1. Relevant information from traceback should be available from confluent-sql to dbt.
2. When running dbt with `--debug`, the effective connection settings should be visible so users can sanity check what the adapter is actually sending. Secrets (`flink_api_key`, `flink_api_secret`) should probably be redacted.

The same principle likely applies to query-time errors in the `exception_handler`, though that path already includes the exception message (it just omits the type).

## References

- `dbt/adapters/confluent/connections.py` - `open()` method is where the connect-time error is currently wrapped
- Related: PR #51 (the 0.1.0/0.3.0 kwarg mismatch that surfaced this gap)

Start in dbt/adapters/confluent/connections.py, especially the open() method where connect-time errors are wrapped, and inspect the exception_handler path for query-time errors. Trace how confluent_sql exceptions reach dbt, then verify that --debug exposes actionable traceback information and effective connection settings while redacting flink_api_key and flink_api_secret.

Written by the indexing model from the issue text.