Fix: --sessions SQL query uses FILTER(WHERE) unsupported by BTQL

[stephenfeather]

Bug

The --sessions command in scripts/braintrust_analyze.py fails with a SQL parse error:

SQL Error: 400 - Expected: end of statement, found: ( at Line: 7, Column: 29

Cause

The list_sessions() function (line 332) uses PostgreSQL's COUNT(*) FILTER (WHERE ...) syntax, which BTQL does not support.

COUNT(*) FILTER (WHERE span_attributes['type'] = 'tool') as tool_count

Fix

Replace with standard SQL SUM(CASE WHEN ... END):

SUM(CASE WHEN span_attributes['type'] = 'tool' THEN 1 ELSE 0 END) as tool_count

Tested and confirmed working against the Braintrust API.