Add ChipInput input primitive (free-form tags, attendees, mentions)

[prakashUXtech]

Context

src/lib/widgets/input/ has a strong primitive set — Combobox, MultiSelect, Search, Textarea, etc. — but no ChipInput: a single-line input that produces a list of chips/tags from free-form text, typically delimited by Enter or comma.

Surfaced during paw-enterprise#220 (calendar event drawer). Attendees was scoped down to a plain text input because no ChipInput exists. The shape comes up across multiple form patterns: attendees, tags, allowed-domains lists, search filter values, mention targets.

What to add

src/lib/widgets/input/ChipInput.svelte — a single primitive that:

• Accepts free-form text in an input field
• Converts to a chip on Enter, comma, or blur (configurable delimiters)
• Renders existing chips inline with the input
• Supports backspace-to-remove last chip when input is empty
• Validates per-chip via an optional validate(value: string) => string | null (return error or null)
• Supports a max-chips cap
• Exposes value as string[] (bindable)

API sketch

<script>
  let { value = $bindable([]), placeholder = '', delimiters = [',', 'Enter'],
        max = Infinity, validate = null, disabled = false } = $props();
</script>

Optional: <ChipInput suggestions={...}> for autocomplete (could route through Combobox if it makes the integration cleaner).

Design considerations

• Match the existing Input.svelte baseline visual / focus ring
• Chips render via the existing display/Chip.svelte for consistency
• Keyboard: Enter to commit, Backspace to remove, Tab cycles focus normally
• Accessibility: aria-multiselectable, each chip has its own remove button with label
• Pasted text with delimiters splits into multiple chips

Acceptance

• Component file at src/lib/widgets/input/ChipInput.svelte
• Test file (mirror MultiSelect.test.ts shape)
• Exported from src/lib/widgets/input/index.ts
• Storybook / playground entry if the repo has one
• Bindable value works as string[]

References

• Triggering PR: qbtrix/paw-enterprise#220
• Adjacent: MultiSelect.svelte (closed set), Combobox.svelte (typeahead), display/Chip.svelte (chip visual)