Phosphor icons and the real store marks

Desktop icons move from lucide to Phosphor (@phosphor-icons/react, per-icon imports, regular weight; fill for the
active nav item, notices and rating stars). The site's icons and the fixture art use Phosphor's own files from
@phosphor-icons/core. App Store and Google Play are shown with their marks from simple-icons (CC0 data), vendored
unchanged by tools/site-icons.ts and rendered as a mask in the neutral text colour next to the store's name; the
trademark note is in docs/desktop.md and the site footer. lucide-react and lucide-static removed. The
no-hand-written-SVG guard allows only the vendored files (byte-equal to their packages) and per-icon Phosphor
imports. Site stylesheet ?v= bumped.

site/img/icons/play.svg

@@ -1,15 +1 @@
-<!-- @license lucide-static v1.55.0 - ISC -->
-<svg
-  class="lucide lucide-play"
-  xmlns="http://www.w3.org/2000/svg"
-  width="24"
-  height="24"
-  viewBox="0 0 24 24"
-  fill="none"
-  stroke="currentColor"
-  stroke-width="2"
-  stroke-linecap="round"
-  stroke-linejoin="round"
->
-  <path d="M5 5a2 2 0 0 1 3.008-1.728l11.997 6.998a2 2 0 0 1 .003 3.458l-12 7A2 2 0 0 1 5 19z" />
-</svg>
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256" fill="currentColor"><path d="M232.4,114.49,88.32,26.35a16,16,0,0,0-16.2-.3A15.86,15.86,0,0,0,64,39.87V216.13A15.94,15.94,0,0,0,80,232a16.07,16.07,0,0,0,8.36-2.35L232.4,141.51a15.81,15.81,0,0,0,0-27ZM80,215.94V40l143.83,88Z"/></svg>