feat(json): add interactive JSON tree viewer with collapse/expand and rainbow colors (#786)

- Add JsonTreeViewer component with collapse/expand for nested objects and arrays
- Add rainbow colors by depth level using CSS color-mix() with syntax theme tokens
- Add virtualization support (@tanstack/react-virtual) for large JSON files (>200 nodes)
- Add JsonTreeView wrapper with Expand All / Collapse All toolbar
- Integrate into FilesView: tree/text toggle button, JSON file detection
- Integrate into ToolPart: auto-detect JSON tool outputs, render as tree
- Integrate into ToolOutputDialog: JSON tree view in expanded dialog
- Add jsonTreeUtils.ts: parse, flatten, path utilities

No new dependencies - uses existing @tanstack/react-virtual.
Colors derived from existing syntax.* theme tokens - works across all themes.

Co-authored-by: Bohdan Triapitsyn <artmore@protonmail.com>

packages/ui/src/components/chat/message/ToolOutputDialog.tsx

@@ -20,10 +20,12 @@ import {
     renderWebSearchOutput,
     formatInputForDisplay,
     parseReadToolOutput,
+    tryParseJsonOutput,
 } from './toolRenderers';
 import type { ToolPopupContent, DiffViewMode } from './types';
 import { DiffViewToggle } from './DiffViewToggle';
 import { VirtualizedCodeBlock, type CodeLine } from './parts/VirtualizedCodeBlock';
+import { JsonTreeView } from '@/components/ui/JsonTreeView';
 
 interface ToolOutputDialogProps {
     popup: ToolPopupContent;
@@ -1184,6 +1186,18 @@ const ToolOutputDialog: React.FC<ToolOutputDialogProps> = ({ popup, onOpenChange
                                     return <DialogReadContent popup={popup} syntaxTheme={syntaxTheme} pierreThemeConfig={pierreThemeConfig} />;
                                 }
 
+                                // JSON tree viewer for generic JSON outputs
+                                const jsonResult = popup.content ? tryParseJsonOutput(popup.content) : { data: null, isJson: false };
+                                if (jsonResult.isJson) {
+                                    return (
+                                        <JsonTreeView
+                                            jsonString={popup.content}
+                                            initiallyExpandedDepth={3}
+                                            maxHeight="70vh"
+                                        />
+                                    );
+                                }
+
                                 return (
                                     <SyntaxHighlighter
                                         style={syntaxTheme}