Resolved `.archive/<tracking>.html` URLs now serve the target file's
bytes inline via http.ServeFile with Cache-Control: no-cache, replacing
the previous 302 redirect to the per-transmittal URL.
Why: external links like `.archive/<tracking>.html#section` are meant
to track the latest revision. A redirect exposes the snapshot URL — any
forwarded link then pins to that snapshot instead of "latest." Serving
in-place keeps the `.archive/` URL stable as the resolver's "current"
target moves over time.
Cache-Control: no-cache is intentional. Each load revalidates against
the on-disk file's Last-Modified/ETag, so when a new revision lands the
resolver picks it and the browser refetches transparently.
ACL is unchanged: enforced on both the `.archive` context directory and
the resolved target file (per-target denial returns 404, not 403, to
avoid disclosing that a tracking number exists in a hidden subtree).
archivehandler_test.go status expectations updated 302 → 200; fixture
bodies adjusted for body-content verification of the in-place serve.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>