PROD-2346: write local container cache on create/update/adopt

[5PK]

Summary

• container-pusher.ts wrote the source→target mapping row after a successful container create, update, or PROD-2307 referenceName-adopt, but never wrote the corresponding local containers/{id}.json disk cache that ContainerMapper.getMappedEntity reads from.
• That gap let a same-run sync (new container + content pushed into it in the same run) hit a false-positive PROD-2309 "container ... no longer exists on the target — it may have been deleted since the last sync" error, since the guard has no way to distinguish "just created this run, not cached yet" from "genuinely deleted since last sync". Self-healed on the next run, but flipped the exit code non-zero for a container that was never actually missing.
• Added a cacheTargetContainer(targetGuid, container) helper (mirrors download-containers.ts's cache-write shape) and call it after all three success paths: create, update, and the PROD-2307 adopt-by-referenceName branch, which has the identical gap.
• saveContainer() returns the full Container type (same shape as getContainerByID()), so the create/update response itself is sufficient to write the cache — no extra API round-trip needed.

Test plan

• Added 3 new tests to container-pusher.test.ts asserting the cache file is written to disk after create, update, and adopt-by-referenceName
• Full src/lib/pushers + src/lib/mappers suite passes (21 suites, 421 tests)

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