Rebuild: coordinator (planner, NNTP pool, spool, prefetcher, leases, rule sets), node API and the edge:node worker

- groups:add / ranges:plan / nodes:create / coordinator:run commands
- the node API: lease, the range's chunks as one framed stream from the
  spool, batches, heartbeat, finish, release (node guard, token per node)
- edge:node: needs COORDINATOR_URL and NODE_TOKEN only (placeholders for
  the rest), posts a batch every 10 chunks, gives its range back on SIGTERM
- releases are gathered per batch: 1.04 chunk rows per release at 10
  chunks per batch (1.35 when built per XOVER chunk)
- partitions are checked per batch instead of remembered

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

lib/nntp/xover_client.ts

@@ -98,6 +98,21 @@ export class XoverClient {
    * compresses (plain replies are deflated here): the seed API passes these to nodes
    * without unpacking them (CONCEPT.md D38). `parseOverviews(unzipSync(raw).toString())`.
    */
+  /** LIST ACTIVE <pattern>: each group's name, high and low article (low is often just 2 on big servers; GROUP gives the real one). */
+  async listActive(pattern: string): Promise<{ name: string; high: number; low: number }[]> {
+    return this.timed(async () => {
+      const reply = await this.command(`LIST ACTIVE ${pattern}`)
+      await this.expect(reply, ['215'])
+      return (await this.plainBody())
+        .split('\r\n')
+        .filter(Boolean)
+        .map((line) => {
+          const [name, high, low] = line.split(' ')
+          return { name, high: Number(high), low: Number(low) }
+        })
+    })
+  }
+
   async xoverRaw(from: number, to: number): Promise<Buffer> {
     return this.timed(async () => {
       const reply = await this.command(`XOVER ${from}-${to}`)