This PR fills a focused set of missing P0 core DOM-parity APIs in @bquery/bquery/core. It rounds out the single-element and collection wrappers with jQuery-style detach, sibling index, child node access, offset-parent/position queries, and outer size helpers.

• Core parity surface

  • Added detach(), index(), contents(), offsetParent(), position(), outerWidth(includeMargin?), and outerHeight(includeMargin?) to BQueryElement
  • Added matching first-element semantics for the same APIs on BQueryCollection
  • Kept return shapes aligned with the existing wrapper style (this for mutating methods, safe defaults for empty collections)

• Sizing behavior

  • Implemented outer size helpers using layout-box semantics via offsetWidth / offsetHeight
  • Added optional margin inclusion for parity with jQuery-style outerWidth(true) / outerHeight(true)

• Shared core helper

  • Moved outer-size calculation into src/core/shared.ts
  • Reused the shared helper from both wrapper classes to avoid duplicated layout logic

• Coverage and docs

  • Added targeted tests for:
    • detach/re-attach behavior
    • sibling indexing
    • text-node-inclusive contents()
    • offset parent / position lookup
    • outer size with and without margins
    • empty-collection defaults
  • Updated docs/guide/api-core.md to document the new methods

Example:

const item = $('#item');

const idx = item.index();
const nodes = item.contents();
const parent = item.offsetParent();
const pos = item.position();
const width = item.outerWidth(true);

item.detach();
document.body.appendChild(item.raw);