docs(book): Add Part VIII — Scala.js and the NPM ecosystem (facades + Vite)

[xerial]

Adds a new Part VIII to The Uni Book on using the JavaScript/npm ecosystem from a Scala.js Uni app — without ScalablyTyped, as requested.

Chapters

• Ch 12 — Calling NPM Modules from Scala.js: hand-written facades with @js.native + @JSImport (default vs named exports), the js.* type vocabulary, the js.Dynamic escape hatch, and a clear-eyed why not ScalablyTyped (a few honest lines beat a generated TS→Scala library for the handful of calls a real app makes).
• Ch 13 — Bundling with Vite: ModuleKind.ESModule so @JSImport emits real imports; npm install; a main.js entry that loads the Scala.js output and lets Vite resolve the bare imports; and the two real-world escape hatches — the @JSGlobal + window bridge and resolve.alias for browser-hostile transitive deps.

Grounded in real code

Patterns come from the wvlet-ui-playground reference you pointed to:

• the verified Koffi.scala facade (@JSImport("koffi", JSImport.Default)),
• the playground's vite.config.js (resolve.alias koffi→stub, base: "./"), main.js (window.MonacoEditor bridge, dynamic import of the Scala.js output), and package.json,
• ModuleKind.ESModule confirmed against both uni's and wvlet's build.sbt.

Wiring

• New Part VIII in the book ToC and the /book/ sidebar.
• Nav re-threaded: ch11 → 12 → 13 → appendices (ch11 closing and appendix-A prev updated accordingly).
• pnpm docs:build passes (dead-link-clean).

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request introduces Part VIII to the documentation, adding Chapter 12 on writing hand-written Scala.js facades for npm modules and Chapter 13 on bundling Scala.js ES modules with Vite. Feedback on the new chapters suggests declaring methods in @js.native traits as abstract without = js.native to prevent compilation errors, and correcting the sbt output paths from scala-3.x to scala-3 to match standard Scala 3 builds.

Important

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[gemini-code-assist]

In Scala.js, members of a @js.native trait must be abstract. Defining a method with = js.native inside a native trait is redundant and can cause compilation errors in some Scala.js versions. It should be declared without a body.

Suggested change

	def query(sql: String): js.Array[js.Any] = js.native
	def query(sql: String): js.Array[js.Any]

[gemini-code-assist]

In sbt, the default output directory for Scala 3 projects is scala-3 rather than scala-3.x. Updating this path to target/scala-3/app-fastopt/ makes the documentation accurate and copy-pasteable for standard Scala 3 builds.

[gemini-code-assist]

Update the dynamic import path to use scala-3 instead of scala-3.x to match the actual directory structure generated by sbt for Scala 3.

Suggested change

	import('./target/scala-3.x/app-fastopt/main.js')
	import('./target/scala-3/app-fastopt/main.js')