kerf next: status 'clean' is misleading for works whose filter resolves to zero beads

[gregberns]

kerf next prints 'clean' as the rank/status for every entry where 'resolved bead_filter matches zero beads in the store'. 'Clean' reads as healthy/passing; the actual state is empty/unfiltered/needs-attention. Rename the status word (empty / unfiltered / needs-attention).
Discovered: docs/kerf-beta-feedback.md — '## kerf next (post-init)' and Surprises item 8.
Severity: MAJOR.

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Migrated from harmonik bead hk-43ate.