feat: Add presigned URL target models and cleanups

[cau-git]

This PR updates the shared docling service datamodels to support upcoming server-managed artifact delivery, cleanly separate internal result construction from existing API response shapes, and tighten the regular convert endpoint request contract while preserving flexibility for future endpoint expansion.

• add a new PresignedUrlTarget and corresponding artifact/result response models so conversion outputs can be represented as per-document downloadable artifact references
• introduce DocumentResultItem plus mapping helpers to separate internal document result handling from legacy wire models such as ExportResult and ConvertDocumentResponse, without changing existing response payloads
• add regular-endpoint-specific request models that exclude S3 sources, so the stricter regular convert contract is modeled explicitly instead of narrowing the global shared source union
• reject ZIP URLs only for the regular HTTP source path by using a regular-only HTTP request subclass, leaving the shared HTTP source model reusable for future endpoints with different rules
• export the new datamodel types and add focused tests covering target parsing, regular endpoint source validation, shared-vs-regular HTTP ZIP behavior, and internal-to-wire result serialization

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

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Codecov Report

❌ Patch coverage is 96.61017% with 2 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/datamodel/service/responses.py	94.73%	2 Missing ⚠️

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[cau-git]

Currently used for S3Target and PutTarget response. How can this be deprecated? PresignedUrlConvertResponse is not going to replace it, since we said that an S3 target cannot list documents produced by default as it may be very very large, need pagination etc.

[cau-git]

Same question as for ExportResult, why is ConvertDocumentResponse and DocumentResultItem both needed? Appears to have 100% overlap.

If any of this is for backward-compatibility, please explain.

[cau-git]

Why is ExportResult needed when we have DocumentResultItem, or vice versa?
The difference seems to be only:

• "content" instead of "document" field, same type.
• kind present on "ExportResult".
  It makes no sense to me. If any of this is for backward-compatibility, please explain.