Detail page polish: sticky view controls + unsupported-state microcopy/tooltips

[elkraneo]

Context

After timeline rollout, discoverability and clarity can improve further.

Idea

Polish interactions with:

• Sticky segmented controls for view mode.
• Better unsupported-state copy/tooltips to explain — cells.

Scope

• Sticky behavior that works on desktop + mobile.
• Tooltip/microcopy component for unsupported entries.

Acceptance Criteria

• View controls remain visible while reading detail content.
• Unsupported states provide concise explanatory context.
• No overlap/z-index regressions with existing header/nav.