H-5850: Fix PandaCSS and single vite.config

[kube]

🌟 What is the purpose of this PR?

• Wrap margin/padding reset in index.html by @layer reset
  • Fixes issues with padding and margin not being applied when using Panda.
• Merge two vite.config files (lib and site) into a single one with two modes.
• Start extracting some styles from some components.

Pre-Merge Checklist 🚀

🚢 Has this modified a publishable library?

This PR:

• modifies an npm-publishable library and I have added a changeset file(s)

📜 Does this require a change to the docs?

The changes in this PR:

• are internal and do not require a docs change

🕸️ Does this require a change to the Turbo Graph?

The changes in this PR:

• do not affect the execution graph

🐾 Next steps

• Extract styles from more components

❓ How to test this?

• Use latest Petrinaut deploy

[kube]

• H-5691: Update Broken Machines example to have some global parameters #8211
• H-5884: Add Panel SubView, with Horizontal and Vertical SubViews containers #8209
• H-5768: Extract styles from all component files in Petrinaut #8205
• H-5768: Quick Simulation in Edit Mode, and disable Simulate temporarily #8195
• H-5850: Fix PandaCSS and single vite.config #8194 👈 (View in Graphite)
• H-5840: SDCPN diagnostics panel with global type-checker #8171
• main

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[cursor]

PR Summary

Unifies Vite config with mode-based lib/site builds and updates/reset styles, extracting component styles into shared css/cva with minor layout tweaks.

• Build/Config:
  • Merge lib/site Vite configs into a single vite.config.ts with mode-based behavior (--mode=lib for library, default for demo site). Adds conditional dts plugin, define shim, and optimizeDeps config; removes demo-site/vite.config.ts. Updates package.json scripts accordingly.
• Styles/UI:
  • Wrap global margin/padding reset in @layer reset in demo-site/index.html; add .petrinaut-root background in src/index.css.
  • Extract and centralize component styles via css/cva for Menu, Bottom Bar (bottom-bar, diagnostics-indicator, toolbar-modes), and mode-selector, with small spacing/shadow/position tweaks.
• Changeset: Add patch note for @hashintel/petrinaut.

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