feat(ui): streamline workspace settings and remove sharing

Unify compact workspace controls and panel transitions, move directory actions into the context menu, and remove backlink UI.

Reorganize settings with searchable sections, per-setting resets, shortcut search, and accurate save feedback.

Remove sharing UI, APIs, authentication helpers, and storage code; provide a transactional cleanup script with retirement tests. Reject directories during orphan image cleanup and cover mixed-batch preservation.

internal/api/themes/black.css

@@ -24,7 +24,6 @@
 /* 绿色按钮使用深色文字，保持按钮的文字对比度。 */
 .rm-btn-primary,
 .rm-btn-primary:hover,
-.rm-segmented button.on,
-.rm-share-password button {
+.rm-segmented button.on {
   color: #101b16;
 }