Clean EnSite payload builder

[bpulluta]

Please check if the PR fulfills these requirements

• CHANGELOG.md is updated
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)
• Any new Django model inputs have also been added to job/test/posts/all_inputs_test.json

What kind of change does this PR introduce?

(Bug fix, feature, docs update, ...)

• Simplified /ensite UI-to-EnLitePy translation.
• Enforces single keys: pChgMax_kW (vehicles), pChgCap_kW (EMS override).
• Deterministic EMS capacity derivation (sum of charger count * power_kW) when no override.
• Remove ambiguity and unused legacy paths.
• Make max charging power changes reliably propagate.
• Provide on-demand introspection without bloating default responses.

What is the current behavior?

(You can also link to an open issue here)

What is the new behavior (if this is a feature change)?

Does this PR introduce a breaking change?

(What changes might users need to make in their application due to this PR?)

Other information:

[Copilot]

Pull Request Overview

This PR refactors the EnSite payload builder for translating UI inputs to EnLitePy format. The changes simplify the schema by enforcing single-purpose keys and improve deterministic behavior for EMS capacity derivation.

Key changes:

• Simplified UI schema with single-purpose field enforcement (pChgMax_kW for vehicles, pChgCap_kW for EMS)
• Deterministic EMS capacity auto-derivation from charger configurations when no override provided
• Added optional debug payload echo feature for troubleshooting

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 7 comments.

File	Description
load_builder/views.py	Major refactoring of payload builder with simplified validation, deterministic capacity derivation, and debug features
CHANGELOG.md	Documentation of changes including schema version bump and new debug functionality

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