feat: introduce business logic layer and element-to-function map

[noraeb]

User Story

As a developer maintaining the bay template editor,

I want a dedicated business logic layer that pre-processes the SCD document and a Map<ElementInSLD, Function[]> to look up functions per element,

So that the SLD and functions layers consume pre-processed data rather than raw SCD details, keeping them simple and maintainable.

Acceptance criteria

• A Map<ElementInSLD, Function[]> is computed once per document change and passed to the SLD and functions layers.
• A business logic layer exists that takes doc and returns ready-to-use substations, bays, equipment, and functions.
• The state updates whenever editCount changes.