docs: add DoclingServeConverter documentation page

[julian-risch]

Related Issues

Part of deepset-ai/haystack-core-integrations#3097

Proposed Changes:

• Adds a dedicated DoclingServeConverter docs page covering the three export modes (MARKDOWN, TEXT, JSON), usage examples (standalone, in a pipeline, async), and additional features (URL conversion, metadata, ByteStream inputs, authentication, custom conversion options)
• Adds DoclingServeConverter to the converters index table in alphabetical order (after DoclingConverter)
• Updates sidebars.js and version-2.28-sidebars.json to include the new page
• Changes applied to both the current docs and the 2.28 versioned docs/sidebars

How did you test it?

• Verify DoclingServeConverter page renders correctly in the docs site
• Verify DoclingServeConverter appears in the Converters sidebar under the correct alphabetical position (after DoclingConverter)
• Check versioned docs (2.28) reflect the same changes
• I ran the code examples with docker and a local Docling Serve container

Notes for the reviewer

Follows the same structure as the DoclingConverter page added in #11213

🤖 Generated with Claude Code

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Project	Deployment	Actions	Updated (UTC)
haystack-docs	Ready	Preview, Comment	May 8, 2026 2:05pm

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.