feat(branding): replace default Tauri icon with the Phokus aperture mark

- regenerate src-tauri/icons from the new branding/phokus-aperture.svg master
- add reusable PhokusMark component (inline SVG, inherits currentColor)
- use it for the titlebar app mark, retiring the placeholder

src/components/PhokusMark.tsx

@@ -0,0 +1,29 @@
+// Phokus brand mark — a camera iris, rendered inline so it inherits `currentColor`
+// and scales to any size. Drive color + dimensions from the className, e.g.
+//   <PhokusMark className="h-4 w-4 text-gray-300" />
+// The full app-icon tile (filled iris on a dark rounded square) lives in
+// branding/phokus-aperture.svg and feeds `pnpm tauri icon`.
+const BLADE = "M0,-4.18 A10,10 0 0 1 6.43,-7.66";
+
+export function PhokusMark({ className }: { className?: string }) {
+  return (
+    <svg viewBox="0 0 24 24" fill="none" className={className}>
+      <g
+        transform="translate(12 12)"
+        stroke="currentColor"
+        strokeWidth="1.5"
+        strokeLinecap="round"
+        strokeLinejoin="round"
+      >
+        <circle r="10" />
+        <path d="M0,-4.18 A4.73,4.73 0 0 0 3.62,-2.09 A4.73,4.73 0 0 0 3.62,2.09 A4.73,4.73 0 0 0 0,4.18 A4.73,4.73 0 0 0 -3.62,2.09 A4.73,4.73 0 0 0 -3.62,-2.09 A4.73,4.73 0 0 0 0,-4.18 Z" />
+        <path d={BLADE} />
+        <path d={BLADE} transform="rotate(60)" />
+        <path d={BLADE} transform="rotate(120)" />
+        <path d={BLADE} transform="rotate(180)" />
+        <path d={BLADE} transform="rotate(240)" />
+        <path d={BLADE} transform="rotate(300)" />
+      </g>
+    </svg>
+  );
+}