Implement Error Toasts

[PauloMFJ]

Overview

Adds a lightweight in-house toaster (foundations/toaster) based on Sonner.

• Stacked toasts that collapse into a scaled pile and fan out on hover/focus, with enter/exit animations and pause-on-interaction
• Click anywhere to dismiss (keyboard-accessible) + auto-dismiss timer
• a11y: labelled aria-live region, per-toast dismiss labels, focus-aware expand/pause
• Reduced motion: identical behaviour, just without durations
• Adds toaster-* color tokens, a type-headline mixin, and a $z-index-toaster token
• Fixes the card export / view-chart actions (onclick → onClick) that silently never fired

Screenshots

[gemini-code-assist]

Code Review

This pull request introduces a stacked Toaster notification system, adds zoom and tool Controls to the Atlas editor, updates the Button component to support multiple sizes, and introduces several new icons and color tokens. Feedback on these changes highlights critical issues: in toaster.tsx, the container height calculation when collapsed creates an invisible pointer-blocking area, and the heights state suffers from a memory leak as dismissed toast heights are never cleaned up. Additionally, in atlas.tsx, a CSS variable is incorrectly used for canvas rendering where static RGB values are required, and in button.tsx, making the new size prop required introduces a breaking change that should be resolved by making it optional with a default value.

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[nick-nlb]

We can discuss the bigger comment and keep it for another PR, but otherwise the one smaller behavioral comment.

Do you mind also taking some screenshots and including them in the description here, and then pinging miss-o-soup to have a look (in case this is completely new UI/UX). Alternatively, since we're meeting tomorrow anyway, you could give it a demo then.

[nick-nlb]

While this currently looks safe as it is because it only ever gets used on the client side, it feels fragile to rely on module state. If toast is ever called accidentally during a server-side render, we could get cross-request contamination.

There's no case of that now, but thinking forward both in terms of this app, but also in terms of reuse of the toast library later (where it might be more of an issue).

What do you think of moving the toast functionality to a React context and completely decoupling it from the server? (This would be a fairly big refactor and so could be a separate PR). In the meantime we could put a guard that prevents toasts from being added if window isn't present.

[PauloMFJ]

I considered using a React context but actually ended up choosing this path to match closer to Sonner's implementation + general DX improvements over needing hook. Happy to put in a guard to prevent toasts being added if window isn't present in the meantime.

Happy to review / move towards context later if it becomes an issue?