Funnel view loads 3× faster on cohorts >500 applicants

What changed

• The funnel page now uses a single streaming query that returns counts for every stage at once.
• Background prefetch warms the cache the moment you open a cohort, so toggling between funnel and pipeline views feels instant.

Measured impact

• Median funnel load on cohorts ≥500 applicants: ~3× faster (1.8s → 0.6s).
• Time-to-first-byte on cold loads: ~40% faster.
• No change to data freshness — the same numbers, served quicker.