sylvactl watch: revamp timeline

This MR aims at improving the timeline report.

It was implemented using Claude Code (various models).

The main goal is to reduce the vertical span, placing more resources on same horizontal space when possible.

A secondary goal is to make visible the dependency critical path by placing resources based on when their last dependency reconciles.

Lots of other things are done in this MR:

• add a dark mode (keep light mode, "auto" is used by default)
• on hover, display all dependency links of the resource under the cursor (both depends-on and dependents)
• add a crosshair to help see the time
• improve how time is displayed (show both absolute UTC time and time relative to start)
• search feature
• display both absolute time and time elapsed since first event
• ability to focus on a resouce (clicking on a resource results in displaying only it's dependencies and dependents resources)
• YAML syntax colorisation and fold/unfold in the detailed resource view

After this change the timeline looks like this (in dark mode):

Compared to what we had before (incomplete because too much to scroll):

Another example from a more complete mgmt cluster deployment:

How to develop this mini-app

This MR includes everything needed to work with this file:

• sample data files
  • you simply need to open the app with your local browser (e.g firefox report.tpl.html) and click "upload data"
• AGENTS.md having agent context to pursue agent-based development