fix: detached glass empty after edge-split drop

[ohxyz]

Problem

After dragging a glass and dropping it onto a pane edge (top/right/bottom/left), clicking the glass's detach button produced an empty detached glass — no title, no content.

Root cause

The edge-split drop path in src/binary-window/glass/drag.js did:

const newPaneSash = this.addPane(sash.id, { position: dropArea, id: oldSashId });
newPaneSash.domNode.append(activeDragGlassEl);

But BinaryWindow.addPane always seeds the new pane with its own empty placeholder Glass. Appending the dragged glass left the pane with two bw-glass elements (empty first, real second). The detach action reads the glass via paneEl.querySelector('bw-glass-content'), which returns the first (empty) match — hence the blank detached glass.

The center-swap path was unaffected.

Fix

Use replaceChildren instead of append, so the relocated pane holds exactly the dragged glass.

Notes

• Verified with a scratch test driving the real onPaneDrop handler (failed before, passed after); full suite green (26/26).
• Also tightens the Comments convention in CLAUDE.md (backtick code keywords).