Rebuild: phase 1 modules from the current app, ordered by pipeline stage

lib/nntp (XOVER client, Xref, GROUP), lib/headers (subjects, file keys,
segments from overview lines; the yEnc path stays behind for phase 2),
lib/release (identity, random names, now in lib), lib/files (aggregator,
volume names), lib/rules (posting tools, owner by priority, release
verdicts), lib/chunks (release chunk codec). Their unit tests came along;
new ones for codec, rules and volumes.

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

lib/headers/index.ts

@@ -0,0 +1,3 @@
+export { parseSubject, type ParsedSubject } from './subject.js'
+export { fileKey, weakFileKey, counterFileKey, looksLikeFilename } from './file_key.js'
+export { segmentFromHeader, type IngestSegment, type OverviewHeader } from './segment.js'