Improve link card layout and refresh missing previews

[brzvsk]

What this changes

Link cards put the page title next to the favicon and give the URL more body lines, bounded in both regular and compact cards. Already-visible favicons refresh when metadata arrives; an earlier missing-icon lookup cannot erase a later successful result.

Visible older links fetch missing metadata when previews are enabled, including when the setting changes while the shelf is open. Capture and backfill share one fetcher and its in-flight deduplication. Disabling previews prevents new backfill requests.

Independent PR; no merge dependencies. Typography remains the current upstream font so the system-font PR can be considered separately.

How you tested it

• Xcode Debug build passed with pinned dependencies and signing disabled.

• Reviewed the existing disabled/resolved/in-flight guards, asynchronous favicon callbacks, and bounded regular/compact card layout; git diff --check passed.

• No engine changes. Live visual/network interaction verification is not claimed because UI automation cannot attach to the isolated demo app.

• Every commit is signed off.

• All three SPM pins are preserved.

[tarikbc]

Merged as 198b42d.

I rebased this onto current main and resolved the ItemCardView conflict, which was your new favicon and title layout replacing the old if/else branch. Took your version, kept the font change from #8 and the favorites changes from #15 that had landed in the same file.

Closing because the rebase changed the SHAs, so GitHub can't match it back to this branch. The work is in. Thanks!