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.go

@@ -142,57 +142,3 @@ func (s *Server) getTheme(w http.ResponseWriter, r *http.Request) {
 		CSS string `json:"css"`
 	}{manifest, css})
 }
-
-// 只有有效分享的访客可读取外观；不返回账户、插件和其他应用设置。
-func (s *Server) publicAppearance(w http.ResponseWriter, r *http.Request) {
-	if _, ok := s.openShare(w, r); !ok {
-		return
-	}
-	settings, err := s.readSettings()
-	if err != nil {
-		internalError(w, r, err)
-		return
-	}
-	out := map[string]any{}
-	for _, key := range []string{"colorMode", "uiFontSize", "fontSize", "contentWidth", "textFont", "codeFont", "lineHeight", "paragraphSpacing", "glassOpacity"} {
-		if value, ok := settings[key]; ok {
-			out[key] = value
-		}
-	}
-	var snippets []struct {
-		ID      string `json:"id"`
-		Name    string `json:"name"`
-		CSS     string `json:"css"`
-		Enabled bool   `json:"enabled"`
-	}
-	if value, ok := settings["cssSnippets"]; ok {
-		if err := json.Unmarshal(value, &snippets); err != nil {
-			internalError(w, r, err)
-			return
-		}
-	}
-	active := snippets[:0]
-	for _, snippet := range snippets {
-		if snippet.Enabled {
-			active = append(active, snippet)
-		}
-	}
-	out["cssSnippets"] = active
-	var theme string
-	if value, ok := settings["theme"]; ok {
-		if err := json.Unmarshal(value, &theme); err != nil {
-			internalError(w, r, err)
-			return
-		}
-	}
-	if theme != "" && theme != "default" {
-		_, css, err := s.readTheme(theme)
-		if err != nil {
-			internalError(w, r, err)
-			return
-		}
-		out["themeCSS"] = css
-	}
-	out["theme"] = theme
-	writeJSON(w, 200, out)
-}