Improve "missing esbuild" error message

Hey there,

while I do think the current error message is quite okay...

Failed to find esbuild. See https://esbuild.github.io/getting-started/#install-esbuild for ways to install esbuild.

https://github.com/purescript/spago/blob/310a7096b0d3e86f6464c667aa2339045d85d505/src/Spago/Build.hs#L452

I'd suggest to extend it:

• Add the information that it is spago that failed to find it. If spago is executed directly it's easy to figure out. But if a project is executed (e.g. with webpack or vite), you see a bunch of error messages and one of them is this, it's not clear where this is coming from.
• Add why or what for esbuild is missing. Again it might not be clear why spago build is working fine, and then another command spago bundle-app is failing. Especially if the user is not directly running the command. So stating that spago relies on esbuild to bundle would be good to know.

Example purescript-react-vite-starter

Suggestion

Here are some suggestions with different wording. If one of them and the change in general is okay, I could open a pull request.

Spago failed to find esbuild, but bundling an PureScript code requires esbuild to be installed. See https://esbuild.github.io/getting-started/#install-esbuild for ways to install esbuild.

Spago was unable to find esbuild, yet esbuild must be installed in order to bundle PureScript code. See https://esbuild.github.io/getting-started/#install-esbuild for ways to install esbuild.

Failed to find esbuild. Spago relies on esbuild to bundle code. See https://esbuild.github.io/getting-started/#install-esbuild for ways to install esbuild.

Start at src/Spago/Build.hs around line 452, where the missing esbuild error is reported. Review how spago bundle-app reaches this message and update it to identify Spago and explain that esbuild is needed for bundling. Verify the revised wording when esbuild is unavailable, including the installation link.