A mirror with peers records the checksums of files that had none, so they are copied too

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

CHANGELOG.md

@@ -32,6 +32,8 @@ APIs change between minors without a deprecation period.
 - **`llmgw mirror add-peer` on a mirror with a machine of its own.** It set the second mirror up and then
   failed for want of the control plane's server.yaml; now it prints the `llmgw ctl config set mirror.peers`
   to run on a control plane.
+- **Models fetched before checksums were kept reach the second mirror.** A mirror kept in step copies only what it
+  can check, and those files had no sha256; a mirror with peers now works theirs out and records them, once.
 
 ## v0.15.2 — 2026-10-29