fix(ci): improve regression error messages

[veksen]

Summary

• Show query preview instead of unhelpful query hash
• Format costs with comma delimiters (e.g., 30,954 instead of 30954)
• Include link to the CI run's query page for easy navigation

This makes regression errors more actionable by providing context about the query and the specific cost increase.

[github-actions]

Query Doctor Analysis

View full run details

25 queries analyzed

2 pre-existing issues

• SELECT "guests"."id", "guests"."session_id", "guests"."username", "guests"."avatar_path", "guests"."color", "guests"."side", "guests"."audio_recording_path", "guests"."audio_recording_public", "gue...
  index assets(event_id, uploader_id, inserted_at desc)
  cost 15,922 → 1,639 (90% reduction)
• SELECT * FROM guest_ip_addresses WHERE ip_address = '127.0.0.1';
  index guest_ip_addresses(ip_address)
  cost 126 → 9 (93% reduction)

_{Using assumed statistics (10000 rows/table). For better results, sync production stats.}