🎨 Palette: Add context-specific ARIA labels to repetitive table actions

[seonghobae]

Provides context-specific aria-label attributes to repetitive action buttons ("Details", "Status JSON") and links ("Open viewer") in the viewer demo UI session history table. It uses the row's document filename to improve screen reader accessibility, ensuring users can differentiate between actions on different rows.

Testing:

• Checked via local Playwright frontend test (verified that aria-label includes the filename).
• Backend tests pass (mvn test).

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PR created automatically by Jules for task 13627136632628306671 started by @seonghobae

[google-labs-jules]

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