Add Plate-powered rich document editor

[beNative]

Summary

• add a Plate-based rich text editor wrapper with HTML serialization, toolbar controls, and scroll syncing
• extend document classification, repository plumbing, and exports with the new rich_text doc type and sample data
• update the prompt editor to toggle between visual/source engines, wiring Plate into preview/export flows and disabling Monaco-only actions when inactive

Testing

• npm run test:markdown

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Codex Task

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Skip flag blocks loading new document content after cursor changes

handleValueChange sets skipNextContentSyncRef.current = true on every editor onChange, even when no content has changed (Slate fires onChange for selection/caret moves). The effect at the top of this component uses that flag to ignore the next content prop update, so switching to a different document after simply moving the cursor leaves the previous document’s HTML rendered. Subsequent edits will then overwrite the newly selected document with the stale content. Consider only setting the skip flag when the serialized HTML actually differs, or resetting it on selection-only changes, so external document changes always replace the editor state.

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