Seed plans fill every uncovered gap, with priorities; cheaper ingest and file storing

- seed:plan plans every part of a group's history no range covers (it
  started below the lowest known range and left a.b.ath's 13 most recent
  months out); seed_ranges.priority orders leases (seed:plan --priority).
- binaries.part_count, kept by the parts insert in the same statement:
  claimCompleted compares it instead of counting parts every batch.
- file_keys: 64-bit hashes of all file keys; FileStore.insert asks it
  before probing every files partition.
- worker:file stores 100 completed binaries per job with set-based queries.

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

tests/functional/seed_api.spec.ts

@@ -134,6 +134,16 @@ test.group('Seed API', (group) => {
     }
   })
 
+  test('ranges of a higher priority are leased first', async ({ client, assert }) => {
+    const token = await SeedOrchestrator.issueToken('priority-node')
+    await db.table('seed_ranges').insert([
+      { group_name: 'alt.binaries.test', start_id: 1, end_id: 100, next_id: 1 },
+      { group_name: 'alt.binaries.test', start_id: 101, end_id: 200, next_id: 101, priority: 1 },
+    ])
+    const leased = await client.post('/api/v1/seed/lease').headers({ authorization: `Bearer ${token}` })
+    assert.include(leased.body().range, { start: 101, end: 200 })
+  })
+
   test('a node inspects a file: lease, probe result, applied here (D41)', async ({ client, assert }) => {
     await QueueService.collectionQueue.drain()
     await QueueService.archiveWalkQueue.drain()