(remote): tighten head-turn warning normalisation and cap its state (follow-up #888) #889

Follow-up of #888 (#885), review minors, low priority.

1. Path pattern too broad. remote-index.js ~304 normalises any text starting with /, not just absolute paths, so projects/foo vs projects/bar and URLs on different hosts merge. The doc says "absolute paths". Anchor the pattern on start-of-text, whitespace or a quote, or fix the doc.
2. Unbounded signature Set. It only empties on recovery, and a message with a bare UUID is never deduplicated. Cap it at about 20 entries.
3. Prune test case. In test/remote-index.test.js, the "1 remaining host" case already passed before (remote): guard per-row cache reads in task snapshots and dedup warnings by cause (#885) #888. Only the 0-host case exercises the new loop. Say so in the test, or drop the case.