chore(atomic): migrate atomic-insight-result-children-template to Lit

[alexprudhomme]

Migrates atomic-insight-result-children-template from Stencil to Lit, following the same patterns established by the search-equivalent atomic-result-children-template.

What changed

• New Lit component — uses ResultTemplateController, @errorGuard(), @mapProperty, and @withTailwindStyles decorators
• Imports from @coveo/headless/insight instead of @coveo/headless (the Stencil original used the less-specific import)
• Unit tests (Vitest + browser mode) covering instantiation, default props, connectedCallback match conditions, getTemplate delegation, render output, and error rendering
• E2E tests (Playwright) for default, nested grandchildren, and conditional template stories
• Storybook stories (3): Default, With nested children (via inherit-templates), With conditions
• MDX documentation with usage examples, template condition semantics, and nested children guidance
• Registration in index.ts, lazy-index.ts, custom-element-tags.ts, and components.d.ts
• Cypress test for the Atomic Insight result panel were removed

Scout camping

• atomic-result-children-template.spec.ts (search sibling): fixed mockResolvedValue → mockReturnValue (getTemplate is synchronous) and .toBeDefined() → .not.toBeNull() (vacuous assertion on querySelector return)

Editorial choices

• allowEmpty kept as false (matching the Stencil original default) rather than setting it to true
• Mock data refactored: extracted child result objects into reusable constants; added nestedFoldedResponse with grandchildren for the nested story
• Module-level mock() instead of mockOnce in beforeEach, so the Storybook Docs page renders all stories correctly (shared harness was being exhausted)
• @internal tag removed — intentional, needed for Storybook custom element manifest generation

Checklist

• 🧪 The component is unit tested
• 🧪 The component includes E2E tests
• 🗑️ Old Cypress tests exclusive to the component are removed
• 📖 The component is documented in storybook with an .mdx file
• ♿ The component complies with the Web Content Accessibility Guidelines. N/A: Template-only component; renders nothing — accessibility depends on slotted content
• 🌐 All strings intended for humans or assistive technology must be localized with i18n. N/A: No user-facing strings
• 📦 The Lit component is exported in the appropriate index.ts and lazy-index.ts files.
• 🎨 CSS parts are documented still accessible. N/A: Component renders nothing; no CSS parts
• 🦥 Slotted Content, public methods and properties are documented
• 🔄 The component outputs the same Angular output as before with Stencil N/A: Template component — not wrapped in Angular
• 🏷️ The component declares the component type in the HTMLElementTagNameMap

https://coveord.atlassian.net/browse/KIT-5481

[fbeaudoincoveo]

This is the last Stencil component we're migrating. We no longer need the Atomic Insight Cypress tests. Bye bye!

[louis-bompart]

o7

[fbeaudoincoveo]

Note that this prop and ifNotDefined are not present in the atomic-result-children-template (i.e., the search version). I'm leaving them here to avoid breaking changes, but there's a discrepancy.