feat: add react-scan integration for performance monitoring

[DeJeune]

What this PR does

Before this PR:

• No built-in way to monitor React component render performance during development

After this PR:

• Adds react-scan integration for visual performance monitoring
• Run pnpm dev:react-scan to start dev server with react-scan enabled
• Shows render counts, unnecessary re-renders, and FPS in a toolbar overlay

Why we need it and why it was done in this way

The following tradeoffs were made:

• react-scan is only enabled via environment variable (RENDERER_VITE_REACT_SCAN=true) to avoid any overhead in normal development
• Integrated into all window entry points (main, mini, selection toolbar/action, trace) for comprehensive coverage

The following alternatives were considered:

• CI integration with performance thresholds - decided against as team felt it was not valuable enough for the complexity

Breaking changes

None

Special notes for your reviewer

• react-scan is a dev-only tool, no production impact
• Usage: pnpm dev:react-scan to enable performance monitoring

Checklist

• PR: The PR description is expressive enough and will help future contributors
• Code: Write code that humans can understand and Keep it simple
• Refactor: You have left the code cleaner than you found it (Boy Scout Rule)
• Upgrade: Impact of this change on upgrade flows was considered and addressed if required
• Documentation: A user-guide update was considered and is present (link) or not required

Release note

feat: add react-scan integration for performance monitoring (run `pnpm dev:react-scan`)

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