docs(core): drop comments the code already says master
Cut anything a reader gets from the line beneath it: a test-file header describing the context object the next statement constructs, an export-map note that would repeat in every handler module, three comments justifying why a test exists where its name already says so, and the restated halves of the pointers into the two handler modules. The empty Sync banner went with them -- the one fact it carried, that getBlob and listBlobs stay behind, belongs on the Blobs banner where that looks inconsistent. What stayed is what the syntax cannot give: the construction order backup depends on, why an unused `await getDid()` is not dead code, why a single-account server answers RepoNotFound for another DID, why an assertion expects a truncated CAR, and how glob threshold keys aggregate. Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>