A missing first article is an inspection result, not a failure

Eweka answers 'no such article' after ~450 ms; a quarter of inspection
requests were for missing articles and each failed job was retried up
to three times. Files get content_type 'missing' instead; homelab also
records it from failure reports of nodes not rebuilt yet.

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

lib/content/sniff.ts

@@ -6,6 +6,8 @@
  * (LOG.md 2026-09-30 (3)): a fixed header, then data with 8 bits/byte of entropy.
  */
 export type ContentType =
+  /** Not sniffed: the server no longer has the file's first article (inspection records it, no retries). */
+  | 'missing'
   | 'nzbe'
   | 'par2'
   | 'rar4'