Create slider form component

[mikesealey]

Description

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Addresses

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Summary by cubic

Added a new Slider form field that lets users select a number with min/max/step, optional icons, and optional value display. Registered it in the builder and manifest, and updated form types to support numeric defaults and typed change events.

• New Features

  • New Slider.svelte using CoreSlider with label, min/max/step, value, disabled, help text, optional value display, and left/right icons (size configurable, clickable to adjust by step). Binds to Field wrapper (NUMBER) and emits onChange.
  • Added "slider" to manifest with settings and static context for value. Enabled in builder palette and lazy-loaded export.

• Refactors

  • Converted bbui Core Slider to TypeScript with typed change events and value handling.
  • Expanded form default value types (FieldDefaultValue) and applied in Field.svelte and InnerForm.svelte. Added parsing/clamping to keep values numeric and within bounds.

^{Written for commit 2eb41ba. Summary will update on new commits.}