When the anonymizer doesn't change a slice's text, the streamer used
to push Buffer.from(out, "utf8") — which loses any invalid-UTF-8 bytes
in the input (replaced by U+FFFD via StringDecoder). Files
mistakenly classified as text (binary blobs without a known extension,
text with stray non-UTF-8 bytes, BOMs) came out corrupted even though
nothing in the term list matched.
Track the raw chunk bytes alongside the decoded `pending`. On flush —
where we have every byte buffered — emit the original buffer directly
when the output equals the input, so a pure passthrough is bit-exact.
In the streaming OVERLAP path, do the same when the decode for that
slice round-trips losslessly; fall back to encoded output otherwise
(unchanged from before for that case).
Also add the "missing_content" locale entry for the
/api/anonymize-preview route.
tdurieux