feat: leftsidebar collapsible tool groups + scroll + resizable width

frontend/src/App.tsx

@@ -149,6 +149,7 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
   const [mobileRightOpen, setMobileRightOpen] = useState(false);
   // Desktop sidebar collapse
   const [leftSidebarCollapsed, setLeftSidebarCollapsed] = useState(false);
+  const [leftbarWidth, setLeftbarWidth] = useState(200);
   const [rightSidebarCollapsed, setRightSidebarCollapsed] = useState(false);
   const [settingsOpen, setSettingsOpen] = useState(false);
   const [activeDrawerTab, setActiveDrawerTab] = useState<DrawerTab>('tool');
@@ -1553,6 +1554,8 @@ const CADEditor: React.FC<CADEditorProps> = ({ projectId, token, onNavigateBack
           onSaveGroupAsBlock={handleSaveGroupAsBlock}
           onGroup={() => handleRibbonAction('group')}
           onUngroup={() => handleRibbonAction('ungroup')}
+          leftbarWidth={leftbarWidth}
+          onWidthChange={setLeftbarWidth}
         />
         <CanvasArea
           cursorPos={cursorPos}

frontend/src/components/LeftSidebar.tsx

@@ -1,4 +1,4 @@
-import React from 'react';
+import React, { useState, useCallback } from 'react';
 import type { LeftSidebarProps } from '../types/ui.types';
 import { SEATING_TEMPLATES } from '../services/seatingService';
 
@@ -56,7 +56,53 @@ const sections: Array<{ label: string; tools: ToolDef[] }> = [
   { label: 'Bestuhlung', tools: sectionBestuhlung },
 ];
 
-const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, selectedTemplate, onTemplateSelect, onCollapse, className, collapsed, onToggleCollapse, onGroup, onUngroup }) => {
+const MIN_LEFTBAR_WIDTH = 140;
+const MAX_LEFTBAR_WIDTH = 400;
+
+const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, selectedTemplate, onTemplateSelect, onCollapse, className, collapsed, onToggleCollapse, onGroup, onUngroup, leftbarWidth = 200, onWidthChange }) => {
+  const [collapsedSections, setCollapsedSections] = useState<Record<string, boolean>>({});
+
+  const toggleSection = useCallback((label: string) => {
+    setCollapsedSections((prev) => ({ ...prev, [label]: !prev[label] }));
+  }, []);
+
+  const handleResizeMouseDown = useCallback((e: React.MouseEvent) => {
+    e.preventDefault();
+    e.stopPropagation();
+    const startClientX = e.clientX;
+    const startWidth = leftbarWidth;
+
+    const handleMouseMove = (ev: MouseEvent) => {
+      const delta = ev.clientX - startClientX;
+      const newWidth = Math.min(MAX_LEFTBAR_WIDTH, Math.max(MIN_LEFTBAR_WIDTH, startWidth + delta));
+      document.documentElement.style.setProperty('--leftbar-w', newWidth + 'px');
+      if (onWidthChange) {
+        onWidthChange(newWidth);
+      }
+    };
+
+    const handleMouseUp = () => {
+      document.removeEventListener('mousemove', handleMouseMove);
+      document.removeEventListener('mouseup', handleMouseUp);
+      document.body.style.cursor = '';
+    };
+
+    document.body.style.cursor = 'col-resize';
+    document.addEventListener('mousemove', handleMouseMove);
+    document.addEventListener('mouseup', handleMouseUp);
+  }, [leftbarWidth, onWidthChange]);
+
+  const renderSectionLabel = (label: string, sectionKey: string) => (
+    <div
+      className="tool-section-label"
+      onClick={() => toggleSection(sectionKey)}
+      style={{ cursor: 'pointer', userSelect: 'none', display: 'flex', alignItems: 'center', gap: '4px' }}
+    >
+      <span className="tool-section-chevron">{collapsedSections[sectionKey] ? '▶' : '▼'}</span>
+      {label}
+    </div>
+  );
+
   return (
     <aside className={`leftbar${className ? ' ' + className : ''}${collapsed ? ' leftbar-collapsed' : ''}`} aria-label="Werkzeugpalette">
       <div className="leftbar-header">
@@ -66,10 +112,12 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, sel
         </button>
       </div>
 
+      <div className="leftbar-content">
+
       {sections.map((section) => (
         <div className="tool-section" key={section.label}>
-          <div className="tool-section-label">{section.label}</div>
-          <div className="tool-grid">
+          {renderSectionLabel(section.label, section.label)}
+          <div className="tool-grid" style={collapsedSections[section.label] ? { display: 'none' } : undefined}>
             {section.tools.map((t) => (
               <button
                 key={t.tool}
@@ -89,8 +137,8 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, sel
 
       {(onGroup || onUngroup) && (
         <div className="tool-section" key="grouping">
-          <div className="tool-section-label">Gruppierung</div>
-          <div className="tool-grid">
+          {renderSectionLabel("Gruppierung", "grouping")}
+          <div className="tool-grid" style={collapsedSections["grouping"] ? { display: "none" } : undefined}>
             {onGroup && (
               <button
                 className="tool-btn"
@@ -119,7 +167,7 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, sel
 
       {activeTool === 'seating-template' && onTemplateSelect && (
         <div className="tool-section" key="templates">
-          <div className="tool-section-label">Vorlagen</div>
+          {renderSectionLabel("Vorlagen", "templates")}
           <select
             className="template-dropdown"
             value={selectedTemplate ?? ''}
@@ -149,7 +197,9 @@ const LeftSidebar: React.FC<LeftSidebarProps> = ({ activeTool, onToolChange, sel
           )}
         </div>
       )}
+      </div>
 
+      <div className="leftbar-resize-handle" onMouseDown={handleResizeMouseDown} />
 
       <div className="leftbar-footer">
         {onToggleCollapse && (

frontend/src/styles.css

@@ -455,14 +455,38 @@ a:hover { text-decoration: underline; }
   flex-direction: column;
   overflow: hidden;
   min-width: 0;
+  position: relative;
 }
 .leftbar-header {
+  flex-shrink: 0;
   padding: var(--spacing-md) var(--spacing-md) var(--spacing-sm);
   border-bottom: 1px solid var(--color-border);
   display: flex;
   align-items: center;
   justify-content: space-between;
 }
+.leftbar-content {
+  flex: 1;
+  overflow-y: auto;
+  -webkit-overflow-scrolling: touch;
+}
+.leftbar-resize-handle {
+  position: absolute;
+  right: -2px;
+  top: 0;
+  bottom: 0;
+  width: 4px;
+  cursor: col-resize;
+  z-index: 10;
+}
+.leftbar-resize-handle:hover {
+  background: var(--color-primary);
+}
+.tool-section-chevron {
+  font-size: 8px;
+  display: inline-block;
+  flex-shrink: 0;
+}
 .leftbar-title {
   font-size: var(--fs-xs);
   font-weight: 600;
@@ -543,6 +567,7 @@ a:hover { text-decoration: underline; }
 .tool-btn.active .tool-btn-kbd { color: rgba(255,255,255,0.7); background: rgba(255,255,255,0.15); }
 
 .leftbar-footer {
+  flex-shrink: 0;
   margin-top: auto;
   padding: var(--spacing-sm);
   border-top: 1px solid var(--color-border);

frontend/src/types/ui.types.ts

@@ -110,6 +110,8 @@ export interface LeftSidebarProps {
   onSaveGroupAsBlock?: (name: string) => void;
   onGroup?: () => void;
   onUngroup?: () => void;
+  leftbarWidth?: number;
+  onWidthChange?: (width: number) => void;
 }
 
 export interface CanvasAreaProps {