Fix tab rendering in TUI components

Replace tabs with 3 spaces for consistent rendering and width calculation:
- Updated visibleWidth() to normalize tabs before measuring
- Updated Text and Markdown components to replace tabs when rendering
- Updated tool-execution display for read/write tools to replace tabs

This fixes background color rendering issues when displaying files with tab indentation.

packages/coding-agent/test.json

@@ -0,0 +1,28 @@
+{
+	"name": "test-file",
+	"version": "1.0.0",
+	"description": "A test JSON file with tab indentation",
+	"author": "coding-agent",
+	"data": {
+		"items": [
+			{
+				"id": 1,
+				"name": "First item",
+				"active": true
+			},
+			{
+				"id": 2,
+				"name": "Second item",
+				"active": false
+			}
+		],
+		"metadata": {
+			"created": "2024-11-11",
+			"tags": [
+				"test",
+				"example",
+				"json"
+			]
+		}
+	}
+}