Render classification label pills for image/audio entries in viewer

[hemanth-asirvatham]

Motivation

• Images displayed in the notebook viewer were showing rating pills but not their classification labels (audio already showed both), and large media-heavy DataFrames make the viewer very slow to render.
• The change aims to surface snippet-style classification labels as compact "pills" for media rows and to ensure category label overrides are respected when rendering header pills.
• Also consider scalability: avoid rendering full content for huge datasets by using the viewer's existing caps or sampling before calling gabriel.view.

Description

• Added a helper _extract_label_pills(snippet_map, max_labels=24) that collects unique snippet strings to show as label pills for a passage. (file: src/gabriel/utils/passage_viewer.py).
• Attach label_pills to each passage payload when media is present so image/audio rows can display classification labels without losing existing behavior. (file: src/gabriel/utils/passage_viewer.py).
• Extended _build_header_html to accept category_labels and label_pills, use category_labels for pretty category pills, and render a new "Labels" pill stack when label_pills are provided. (file: src/gabriel/utils/passage_viewer.py).
• Wired the header rendering to pass category_labels and label_pills for each entry when assembling the viewer HTML payload; no public API surface changes to view(...) parameters. (file: src/gabriel/utils/passage_viewer.py).

Testing

• No automated tests were executed as part of this change.
• Recommend manual / notebook smoke checks: call gabriel.view on a small DataFrame containing image/audio cells with snippet-style classification columns and verify header shows both category pills and the new Labels stack; for large datasets, validate responsiveness using max_passages or by sampling the DataFrame (e.g., df.sample(10)).

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Codex Task

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