Improve dense table readability with sticky headers and column presets

[johnsmccain]

Summary

Implements the following dashboard improvements:

• [2026 UX] Improve dense table readability with sticky headers and column presets #880: Add sticky table headers, density controls, and saved column presets for transactions and analytics tables.
• [2026 UX] Add print-optimized views for compliance and audit pages #881: Add print-optimized layouts and CSS for compliance and audit pages.
• [2026 Mobile] Add biometric unlock for cached read-only session data #884: Add biometric protection for cached read-only session data on supported mobile platforms.
• [2026 PWA] Cache critical documentation pages for offline reference #888: Add service worker caching for critical documentation and guides for offline access.

Verification

• Added automated tests covering primary flows, boundary conditions, unsupported environments, and failure paths.
• Updated relevant documentation and compatibility/security guidance.
• Verified existing functionality remains intact and CI checks pass.

Closes #880
Closes #881
Closes #884
Closes #888

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