Release v1.5.0

[marcop135]

Summary

Minor release. Use Excalidraw's native Mermaid instead of our custom modal, plus mobile toolbar UX fixes.

• Enhance: Drop the custom Insert > Mermaid modal and adapter; use Excalidraw's built-in Mermaid to Excalidraw (More tools menu), which parses the same diagrams into native editable shapes.
• Fix: On phones, keep the action bar above Excalidraw's bottom bar while editing so Export stays reachable in any tool state.
• Style: Drop the GitHub link from the crowded phone bottom bar; it stays in the hamburger menu and on the desktop toolbar.
• Enhance: Show the app name beside the version in the hamburger menu (draw v1.5.0).
• Build: Drop the now-unused @excalidraw/mermaid-to-excalidraw direct dependency; Excalidraw still bundles its own copy.
• Docs: Correct the README usage, project structure, and tech-stack notes to reflect Mermaid moving to Excalidraw's native menu.

Test plan

• npm run build
• npm run lint
• npm test (28 pass)
• Verified in browser: Insert menu = LaTeX + Markdown, mobile export reachable while drawing, GitHub gone from phone bar, hamburger shows draw v1.5.0, native Mermaid to Excalidraw intact.