Writes translation overrides for an owned page and one configured, non-default target locale. Send the entries read from GET with translation replaced; source and targetGeneration must be the values GET returned.

• Only Translation rows change. Base page content, its items and every other locale are untouched.
• The project default language is rejected (400): it is the source other locales translate from.
• Each entry is compare-and-set on both its source and its targetGeneration, so a delayed agent can never overwrite a source the merchant edited or a newer translation another writer stored. Refused entries are counted in stale and were not written; re-read and resubmit them. applied + stale = requested.
• translation: "" clears a key, keeping the tombstone row that distinguishes "cleared" from "never translated".
• targetGeneration is required on every entry (null when GET returned null); omitting it is a 400, not a blind write.
• At most 250 entries per request; duplicate itemId + key pairs are rejected.
• A request that applies nothing advances no project revision and flushes no cache.
• If the write committed but cache invalidation failed, the response is a 500 whose message states how many entries were applied. Verify with GET; retrying the same entries will not flush the cache, because they then lose the target compare-and-set as no-ops.

Required scope: content:write