Auto-fill program item technical name (slug) from title

When creating a program item, filling in the **Technical name** (slug) field is repetitive — it is typically derived from the title by lowercasing and replacing spaces/special characters with hyphens.

## Requested behaviour

When the user types or pastes into the **Title** field and the **Technical name** field is still empty (has not been manually edited), automatically populate the technical name with a correctly formatted slug.

Example: pasting `"Visual Novel -pelit vuonna 2026 - Miten ja miksi?"` → auto-fills `visual-novel-pelit-vuonna-2026-miten-ja-miksi`

The auto-fill should stop overwriting once the user has manually edited the technical name field.

## Complications

The form currently uses `SchemaForm`. It supports dynamic behaviour through client components implementing a single field type, but there is no precedent for dynamic behaviour spanning multiple fields.

Here we would need to refer the value of `title` in a dynamic field for `slug`. While not technically impossible, it seems rather complex to do while still maintaining a sensible level of abstraction.

Then again, this same need repeats in many other places that have slugs as well:

* Program items (this one)
* Schedule items (currently hidden from UI, but they do have slugs based on program item slug)
* Questions on a form
* Dimensions and dimension values

## Related

See also #564 (auto-suggest technical names for survey fields — same concept, different context).

## Background

Reported by Desucon Frostbite 2026 program management.