Seed orchestrator: remote nodes lease ranges and post results over HTTPS

- seed_nodes (hashed bearer tokens) and seed_ranges (planned ranges with
  lease, resume point and counts); migration …140.
- SeedOrchestrator: lease (oldest plan first, FOR UPDATE SKIP LOCKED; a
  lease without a batch for 15 min passes to the next node and resumes at
  next_id), batch (stores files and fragments, moves next_id), finish,
  release, plan (from below live indexing / the backfill / earlier plans
  down to N days back; takes over the group's backfill), status.
- Seed API under /api/v1/seed (lease, ranges/:id/batches|done|release,
  status) behind a node-token middleware; JSON bodies up to 64 MB after
  gzip.
- seed:node runs a node: no database or Redis, outgoing HTTPS only, N
  connections, gzip batches, retries for network errors and 5xx, drops a
  range on 409, gives its ranges back on SIGTERM. seed-node/ has a compose
  file that builds the image from this repository.
- seed:token, seed:plan, seed:status for the operator. Header parsing moved
  to lib/ingest and the range loop to lib/seed/runner, shared by seed:range
  and seed:node.

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

seed-node/compose.yaml

@@ -0,0 +1,18 @@
+# A seeding node (CONCEPT.md D38): leases article ranges from the seed API over
+# HTTPS, indexes their headers over its own NNTP connections, and posts the
+# results back. Outgoing connections only. Builds the indexer image straight
+# from the git repository.
+#
+#   cp node.env.example node.env   # fill in SEED_TOKEN and the NNTP account
+#   docker compose up -d --build
+name: usenet-seed-node
+
+services:
+  seed-node:
+    build: https://gitea.exp.sforum.nl/daan/usenet-indexer.git#master
+    image: usenet-seed-node:latest
+    command: ["node", "ace", "seed:node"]
+    env_file: node.env
+    restart: unless-stopped
+    # On SIGTERM the node gives its ranges back (resumed from the last batch elsewhere).
+    stop_grace_period: 60s