feat(gui): redesign the Shared with Me page

Show only sections with content, invitations first, and an empty state
when nothing is shared. Rows drop the mount path from the subtitle, show
access as a tinted pill (Can view / Can edit / Can manage) and move
Open, Show in My Files and Leave into a menu. The invitations banner is
gone now that invitations lead the page.

crates/pdfs-gui/resources/style.css

@@ -80,3 +80,6 @@ progressbar.browser-status-meter trough, progressbar.browser-status-meter progre
 .album-card:hover .album-cover { box-shadow: 0 10px 26px rgba(0, 0, 0, 0.5); }
 .album-card:hover .photo-thumb { transform: scale(1.05); }
 .view-switch button { padding-left: 18px; padding-right: 18px; }
+
+/* Shared with Me: what a share lets me do, as a tinted pill beside the name. */
+.role-pill { padding: 2px 10px; border-radius: 999px; font-weight: 600; color: var(--accent-color); background-color: color-mix(in srgb, var(--accent-bg-color) 16%, transparent); }