Update browser tab with flowchart title

## Pull-request Checklist > 🚨 Don't forget to **Squash & Merge** - [ ] Docs updated - [ ] QA on mobile - [ ] Dark Mode - [ ] GA Instrumentation - [ ] Translations **Why:** To improve user experience when editing multiple flowcharts. Browser tabs will now display the active flowchart's name, making it easier to distinguish between different open flowcharts. **What:** Implemented dynamic page titles using `react-helmet` in `FlowchartHeader.tsx`. The title format is now `<flowchart name> - Flowchart Fun`, updating live with the current flowchart's name. --- <a href="https://cursor.com/background-agent?bcId=bc-af9073c7-2cd6-41dd-a2a8-97be20e87b6c"><picture><source media="(prefers-color-scheme: dark)" srcset="https://cursor.com/open-in-cursor-dark.svg"><source media="(prefers-color-scheme: light)" srcset="https://cursor.com/open-in-cursor-light.svg"><img alt="Open in Cursor" src="https://cursor.com/open-in-cursor.svg"></picture></a>&nbsp;<a href="https://cursor.com/agents?id=bc-af9073c7-2cd6-41dd-a2a8-97be20e87b6c"><picture><source media="(prefers-color-scheme: dark)" srcset="https://cursor.com/open-in-web-dark.svg"><source media="(prefers-color-scheme: light)" srcset="https://cursor.com/open-in-web-light.svg"><img alt="Open in Web" src="https://cursor.com/open-in-web.svg"></picture></a>