feat: Add colorization based on health level for panels and toolbar

[hunzlahmalik]

• Colorize the minimized DDT icon #1395

Description

This PR introduces a unified health/alert state for Django Debug Toolbar panels and updates the UI to reflect panel.
The name health is debatable, but the alert was already taken by the panel.

Key Changes

• Adds a ToolbarHealthLevel enum (NONE, WARNING, CRITICAL) for numeric health states.

• Adds a health_level property to the base Panel class, allowing panels to report their health status.

• Implements health_level in AlertsPanel and SQLPanel for alert and slow query detection.

• The toolbar now computes the maximum health level across all panels and uses it to color the hidden toolbar handle.

• UI Updates:

  • Panel buttons and the hidden toolbar handle use new CSS classes and colors based on health level.
  • Adds CSS variables and styles for warning and critical states.

Warning	Warning on Hover	Critical	Critical on Hover

Critical on Panel	Warning on Panel

Motivation

• Improves user experience by visually highlighting issues in the toolbar.

Checklist:

• I have added the relevant tests for this change.
• I have added an item to the Pending section of docs/changes.rst.
• Add to Documentation

[hunzlahmalik]

@matthiask @tim-schilling

I'll be writing the testcases for this. It would be great if you could take a look at it before testcases.

Thanks!

Edit: You can also suggest how to compute health(debatable name) across other panel profiling, time etc...