Update eca-webview: flat prompt-area in browser side view

Bump eca-webview to 8da23d4 ("Scope prompt-area card borders to
eca-desktop only"). The modal-card prompt treatment (full 4-side
border, rounded corners, drop-shadow) was added for eca-desktop's
wide window but read as visual noise inside the browser side-view
layout, where the surrounding chrome already supplies framing.
eca-webview now scopes that treatment to [data-editor="desktop"]
only — eca-web continues to identify itself as "web" and gets the
flat prompt-area on every visit.

🤖 Generated with [eca](https://eca.dev)

Co-Authored-By: eca-agent <git@eca.dev>

Author: ericdallo