Fix: resolve {model} in filters, add metric-named output column

_strip_model_prefixes now replaces {model} with the actual model name
before sqlglot parsing, so placeholder-based filters no longer leak
literal {model} tokens into WHERE clauses.

Multistep funnel output now includes the last-step count aliased to
the metric name, so ORDER BY metric_name works without runtime errors.

Author: nicosuave