Add energy trends and minor UI enhancements

[PardhavMaradani]

Changes made in this Pull Request:

• Add support for Energy value trends
• Add disconnected overlay when dashboard server unavailable
• Add option to save column preset layouts as default

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

---

This PR adds the missing support for calculating and displaying energy trends. The following minor UI enhancements were made:

• Added a disconnected overlay when the dashboard server is not running / available
• Added an option to save preset columns as default layout (to make them editable / customizable)

[read-the-docs-community]

Documentation build overview

📚 mdadash | 🛠️ Build #33322548 | 📁 Comparing d9fdead against latest (d0dbbe5)

  🔍 Preview build  

8 files changed · + 2 added · ± 6 modified

+ Added

• autosummary/mdadash.backend.kernel.utils.html
• _modules/mdadash/backend/kernel/utils.html

± Modified

• genindex.html
• py-modindex.html
• _modules/index.html
• autosummary/mdadash.backend.kernel.core.html
• autosummary/mdadash.backend.kernel.html
• _modules/mdadash/backend/kernel/manager.html

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (d0dbbe5) to head (d9fdead).

Additional details and impacted files

Components	Coverage Δ
frontend	100.00% <100.00%> (ø)
backend	100.00% <100.00%> (ø)

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