[doc](lakehouse) Document timestamp compatibility changes

[Gabriel39]

What problem does this PR solve?

Related Doris PR: apache/doris#65446

The Doris change updates timestamp handling in FileScannerV2 and Parquet export, but the user-visible compatibility rules and migration options were not documented. Without this context, users can accidentally introduce an eight-hour shift while trying to compensate for legacy Parquet INT96 writer behavior.

What is changed?

• Document that FileScannerV2 preserves raw Parquet INT96 wall-clock fields by default, while Parquet INT64 logical timestamps retain their standard semantics.
• Document the Hive Catalog and external-file TVF compatibility property hive.parquet.time-zone, including validation, examples, scope, V1/V2 behavior, and TIMESTAMPTZ handling.
• Explain why the property is Catalog-wide for Hive INT96 columns mapped to DATETIMEV2, and recommend separating files written with different conventions.
• Document round-half-up conversion from ORC nanoseconds to Doris microseconds, including second carry and conservative predicate pruning.
• Correct the Parquet export property name to enable_int96_timestamps and describe its default, INT96/INT64 result, and asynchronous Export persistence.
• Keep the English and Simplified Chinese current documentation synchronized.

Only current documentation is updated because apache/doris#65446 targets unmerged master behavior. Published 4.x, 3.x, 2.1, and Japanese documentation are intentionally unchanged.

Validation

• git diff --check — passed.
• yarn docs:features:changed — passed with no findings.
• yarn docs:i18n-sync:changed — English/Chinese current pages are synchronized; expected warnings remain for intentionally unchanged published versions and Japanese docs.
• yarn docs:links:changed / yarn docs:lint:changed — no new link issues from this change; the commands report existing missing Hive Catalog anchors and existing repository-wide SEO/Markdown findings.
• yarn key-features:generate
• ./local_dev.sh build-all --versions current --skip-install --max-mem 8192 — generated English and Chinese current site output; the build reports existing repository-wide broken-link warnings.