Add timeline mode for signal events and full note viewing

[evkw]

Problem

Long event notes are currently truncated in the Signal Detail event list, and there is no way to view the full note.

The table/list UI is useful for scanning many events, but it is not ideal when reviewing the history of a long-lived signal. For those cases, I need to understand the sequence of events over time and inspect the full context of each update.

Proposed Solution

Add a horizontal timeline mode to the Signal Detail page for browsing signal events.

Requirements

• Keep the existing event list/table available for quick scanning.
• Add a timeline view for signal events.
• Events should be ordered chronologically.
• User can navigate events using:
  • Left arrow = previous event
  • Right arrow = next event
• Selected event should show:
  • Full note text
  • Event type
  • Created date/time
  • Optional link
• Long notes must be fully readable without truncation.
• Timeline should work well for long-lived signals with many events.
• Current event list should either:
  • provide an expand/view-full-note affordance, or
  • link/select the event in timeline mode.

UX Notes

The timeline should help answer:

• What happened first?
• What changed over time?
• What was the latest meaningful update?
• Why was this signal resolved or collapsed into another signal?

This should be especially useful for signals that live across multiple days or weeks.

Acceptance Criteria

• Long event notes can be read in full.
• Signal Detail supports a timeline-style event view.
• Keyboard left/right navigation works between events.
• Selected event displays full detail.
• Existing event list remains usable for scanning.
• No event context is hidden permanently behind truncation.