Content inspection and archive walks on seeding nodes (relay)

Inspection is split into prepare (database), probe (lib/content/probe:
downloads, decoding and parsing, no database) and apply (database).
worker:collection runs all three; seed:node with SEED_INSPECTORS leases
jobs from the same queues through the seed API (BullMQ manual leases),
fetches articles through the seed API and posts the probes back.

A node now needs only SEED_URL and SEED_TOKEN: the settings the app
requires but a node never uses get placeholders for seed:node.

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

lib/rar/index.ts

@@ -4,3 +4,5 @@
  */
 export { parseRarHeaders, rarFormat, decodeRar4Name, storedEntryData, type RarInfo, type RarEntry } from './parse.js'
 export { walkRar, type VolumeReader, type RarWalk } from './walk.js'
+export { SegmentReader, type BodyFetcher } from './segment_reader.js'
+export { extractEntry } from './extract.js'