feat(desktop): performance and clipboard pages, a scrolling tile grid

The tile grid sits in a Flickable capped at three rows, so the fourth row
the new modules bring scrolls inside that box instead of eating the
notification space; a thin accent bar in the margin shows only when a row
is hidden. Tiles are reordered with the everyday ones first.

Performance shows the island's PerfPanel in a Page, with a tile line of CPU
and RAM and the warning dot. Perf.detailed is now a count of live PerfPanel
instances instead of a binding in the status pill: the island and the drawer
both host the panel, and a bool with two writers would let one clear it
under the other.

Clipboard reads cliphist when its page opens: search, copy on click or
Enter, delete per row, clear all behind a 3 second confirm, image entries as
thumbnails decoded once onto tmpfs. Entries reach sh as $1, never inside a
command string. A copy closes the drawer through a new Page.dismiss signal
the drawer connects like back.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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