feat: upgrade to Excalidraw 0.18.0 with legacy file compatibility

[Technophobe01]

Summary

Closes #423

Upgrades the embedded Excalidraw library from 0.17.x to 0.18.0 with full backward compatibility.

Changes

Build System Migration

• Migrated from react-scripts (Webpack) to Vite for faster builds and better ES module support
• Updated TypeScript configuration for Vite compatibility
• Set "type": "module" in package.json for ESM support

Excalidraw 0.18.0 Compatibility

• Updated @excalidraw/excalidraw to 0.18.0
• Added required CSS import for new Excalidraw styles
• Self-hosted fonts with EXCALIDRAW_ASSET_PATH (no CDN dependency)
• Fixed IDE theme integration with Excalidraw wrapper

Legacy File Support

• Added preprocessing for older Excalidraw file formats (boundElements, frameId, lineHeight fixes)
• Fixed embedded SVG/PNG scene loading and encoded payload handling
• Fixed font loading for deprecated fonts (Virgil, Helvetica, Cascadia)

Test Plan

• Verified on macOS (IntelliJ IDEA, PyCharm)
• Tested with legacy files from 0.15.x and 0.17.x
• All file types work: .excalidraw, .excalidraw.svg, .excalidraw.png

[bric3]

Hello, sorry for the delay, I was off, then had to "unpile" stuff at work.

I haven't looked at the code yet.

But there are still a few issues, and I don't think Claude solved them

• Opening hello.svg appear to work, but should use the IDE theme mode (dark or light) by default.

  • Also unsure if it's Excalidraw 0.18.0 with it's new format, but opening it, and just doing it modifies this file. This might be an unavoidable side-effect.

• Opening random.png => simply erase the "content" of the file, i.e. it rewrites the PNG image with nothing inside.

• Opening random.svg => raises the error, meaning it can't recognize this file.

  java.lang.Throwable: random.svg: [LOGSEVERITY_ERROR][https://excalidraw-jetbrains-plugin/assets/index-DPVffEDG.js:40685]:
  Error loading file: Error: Error: invalid file
  	at com.intellij.openapi.diagnostic.Logger.error(Logger.java:376)
  	at com.github.bric3.excalidraw.editor.ExcalidrawWebViewController$initJcefPanel$5.onConsoleMessage(ExcalidrawWebViewController.kt:221)
  	at com.intellij.ui.jcef.JBCefClient$3.lambda$onConsoleMessage$4(JBCefClient.java:301)
  	at com.intellij.ui.jcef.JBCefClient$HandlerSupport.lambda$handle$0(JBCefClient.java:733)
  	at java.base/java.lang.Iterable.forEach(Iterable.java:75)
  	at java.base/java.util.Collections$SynchronizedCollection.forEach(Collections.java:2131)
  	at com.intellij.ui.jcef.JBCefClient$HandlerSupport.handle(JBCefClient.java:733)
  	at com.intellij.ui.jcef.JBCefClient$HandlerSupport.handleBoolean(JBCefClient.java:738)
  	at com.intellij.ui.jcef.JBCefClient$3.onConsoleMessage(JBCefClient.java:300)
  	at jcef/org.cef.CefClient.onConsoleMessage(CefClient.java:354)
  

  Some other time the excalidraw editor is simply blank.

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Please avoid closing and re-oping a new PR, this makes things difficult to review.

[Technophobe01]

Let me take a look at the code and check against your comments. As an aside, I may have do / undo working still noodling on two edge cases.