[refactor] Replace ArtifactPanel hand-rolled links-toggle with Collapsible primitive

[fedorovvvv]

Source: PRD-018 SC-2 audit, Frontend [W3].

template/src/widgets/artifact-panel/ui/ArtifactPanel.svelte:249-291

The Outgoing/Incoming links disclosure is hand-rolled: manual aria-expanded, manual chevron, custom <button> + {#if expanded}. The shared/ui catalogue ships Collapsible (and Accordion) which deliver:

• Built-in aria-controls ↔ region wiring.
• Slide animation that the current implementation lacks.
• Focus management on collapse/expand.
• Less custom code in the widget.

Fix

Swap the two disclosures to:

<Collapsible bind:open={outgoingExpanded}>
  <CollapsibleTrigger ...>Outgoing →</CollapsibleTrigger>
  <CollapsibleContent>...</CollapsibleContent>
</Collapsible>

Or use <Accordion type="multiple"> to bind both Outgoing+Incoming together with a single state.

Acceptance

• Both disclosures use the primitive.
• Keyboard: Enter/Space toggle expand; focus stays on trigger.
• Visual smoke (light + dark) passes.
• Auto-collapse on id change still works (see related issue on the auto-collapse $effect).

Audit traceability

• Reviewer: Frontend, score 6.5/10

[fedorovvvv]

Fixed in branch `develop` as part of PRD-019 Wave 3.

What changed (`template/src/widgets/artifact-panel/ui/ArtifactPanel.svelte`)

• Replaced the two hand-rolled disclosures (Outgoing / Incoming) with `` / `` / ``.
• Built-in `aria-controls` wiring + focus management come for free from bits-ui.
• Auto-collapse on artifact id change still works (see [bug] ArtifactPanel auto-collapse $effect re-fires on poll due to implicit outgoing.length dep #96 — $effect now untracked properly so the 10s poll doesn't undo user toggles).

Acceptance

• Both disclosures use the Collapsible primitive.
• Keyboard: Enter/Space toggle expand; focus stays on trigger (bits-ui default).
• Visual smoke (light + dark) — passes.
• Auto-collapse on `id` change still works.
• `npm run check` clean.

[fedorovvvv]

Resolved by PR #100 (merged into develop as merge commit 6f498b9). Will reach main with the next release/v* cycle.