Add /export command to export sessions as self-contained HTML

- Add exportSessionToHtml function that generates beautifully formatted HTML exports
- HTML includes session metadata, all messages, tool calls, tool results, thinking blocks, and images
- Support for ANSI color codes in tool output (converted to HTML)
- Self-contained with inline CSS (dark theme, responsive design, print-friendly)
- Add /export slash command to TUI with optional filename parameter
- Add agent and coding-agent to dev script for watch mode
- Increment coding-agent version to 0.6.1

Usage: /export [optional-filename.html]

packages/coding-agent/package.json

@@ -1,6 +1,6 @@
 {
 	"name": "@mariozechner/coding-agent",
-	"version": "0.6.0",
+	"version": "0.6.1",
 	"description": "Coding agent CLI with read, bash, edit, write tools and session management",
 	"type": "module",
 	"bin": {