fix(subheader): prevent scroll jump when opening igc-select

[dobromirts]

Closes #81

Clicking the package/version igc-select in the sticky subheader while scrolled down caused the page to jump.

1. AbortController - adds a disconnectedCallback and aborts all listeners on each connectedCallback, preventing listener accumulation on Astro View Transition page navigations (root cause of the regression)
2. igcInput.focus patch -permanently patches igc-input.focus() inside igc-select's shadow to always pass preventScroll: true, eliminating the scroll on programmatic focus calls (_selectItem, _handleEscape, etc.) that fire on item selection / close
3. scroll-behavior: auto guard - DocsLayout sets scroll-behavior: smooth on , causing the browser's click-triggered focus scroll to animate over multiple frames. Forcing auto on pointerdown and restoring after focusin makes the scroll instant so the savedY correction fires in the same frame with no visible flicker

[rkaraivanov]

@dobromirts

Regarding point 2, that should be logged as an issue in the select component itself and fixed there IMO.

Also, since we depend on igniteui-webcomponents, can we use Lit to encapsulate all the vanilla JS stuff around some of the astro components into a bunch of custom elements (that is no Shadow DOM), just to make easier to template, bind and keep up state more structured.

Feel free to ping me for additional discussion.