Rebuild: merger rounds with one neighbour query, a cursor and a time budget; planning skips failing groups

The neighbour check was three queries per file (~2,000 files/minute); now
one per round of 20k files, with a cursor so waiting files don't take
every round's places, and rounds until nothing is left or 30 s. On the
dev backlog (old-style fragments): ~18k files/minute in the 30 s budget;
at full throughput the new fragment rule leaves ~1,200 files/minute.
A group that fails GROUP (gone from the server) no longer stops planning
the others; edge:bench's groups are inactive.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

commands/edge_bench.ts

@@ -101,7 +101,8 @@ export default class EdgeBench extends BaseCommand {
     let rangeId = 0
     let nodeId = 0
     if (this.store) {
-      const [g] = await db.table('groups').insert({ name: `bench:${group}:${Date.now()}`, priority: 1_000_000 + (Date.now() % 1_000_000) }).returning('id')
+      // Inactive: the coordinator neither plans nor leases it.
+      const [g] = await db.table('groups').insert({ name: `bench:${group}:${Date.now()}`, priority: 1_000_000 + (Date.now() % 1_000_000), active: false }).returning('id')
       const [n] = await db.table('nodes').insert({ name: `bench-${Date.now()}` }).returning('id')
       nodeId = Number(n.id)
       const [r] = await db.table('ranges').insert({ group_id: g.id, start_id: start, end_id: end, next_id: start, status: 'leased', node_id: nodeId }).returning('id')