Track standalone TestWatchCoordinationWindows failure #4004

Summary

go test ./pkg/tbtc -run TestWatchCoordinationWindows -count=1 fails standalone with:

timeout waiting for windows: got 1, expected 2

Evidence

• The failure reproduces outside the FROST DKG coordinator changes in PR Implement FROST DKG coordinator #4003.
• PR Implement FROST DKG coordinator #4003 does not modify pkg/tbtc/coordination.go or pkg/tbtc/coordination_test.go.
• git diff --name-only origin/feat/frost-schnorr-migration-scaffold...HEAD -- pkg/tbtc/coordination.go pkg/tbtc/coordination_test.go pkg/tbtc/coordination* produced no output.
• git blame -L 130,200 -- pkg/tbtc/coordination_test.go shows the original test lines from 389991ca49 and timeout/channel handling from 613c068e40.

Why track this separately

PR #4003 review noted this as a pre-existing, unrelated failure. Tracking it separately keeps the FROST DKG coordinator PR focused while preserving a visible follow-up for the coordination-window test behavior.