Replace npm with pnpm (#136)

## Summary

[`pnpm`](https://pnpm.io/) vs `npm`
- Pros
  - Integrated (interactive) version manager
    - `pnpm up-deps` / (aliased `pnpm update -r -i --latest`)
- `npm outdated` / `npm update --save-dev --save` only adhere to
`package.json` semver
- Must manually modify versions for major versions (ex. Vite 5 => 6)
- Can use [`npx
npm-check-updates`](https://github.com/raineorshine/npm-check-updates)
package to provide similar functionality
  - Efficient Disk space
  - Workspace support
- npm added
[support](https://docs.npmjs.com/cli/v8/using-npm/workspaces) but not
aware of any major projects using it
  - Typically [faster installs](https://pnpm.io/benchmarks) than npm
  - Slightly better developer ergonomics (`pnpm dev` vs `npm run dev`)
- [Used](https://pnpm.io/users) by many large projects/companies (Vite,
Svelte, etc)
- Cons
  - Additional install (`npm` included with Node.js)
- Synk
[support](https://docs.snyk.io/supported-languages-package-managers-and-frameworks/javascript/javascript-for-open-source?_gl=1*1gi9low*_gcl_au*MTA2ODIxOTcxNy4xNzM0Mzg4MTY2*_ga*MTEzMzg2NzM3NS4xNzM0MDIzMDg5*_ga_X9SH3KP7B4*MTczNDU0MzI4Mi40LjAuMTczNDU0MzI4Mi4wLjAuMA..#pnpm)
is currently in
[preview](https://app.snyk.io/org/varant-zlai/manage/beta-features)
- package version overrides not currently applying with Synk
(configuration, preview status of integration, ...). Likely because snyk
is configured to scan `package-lock.json` (npm) and not `pnpm-lock.yaml`
(pnpm).
([here](https://app.snyk.io/org/varant-zlai/project/f4bdc116-d05b-4937-96b5-b1f9a02872e5))

---


![image](https://github.com/user-attachments/assets/3fff95c6-f100-4083-9463-042b27763d1f)


![image](https://github.com/user-attachments/assets/decb6b45-60d0-40b5-a37a-803dd6deb302)


## Checklist
- [ ] Added Unit Tests
- [x] Covered by existing CI
- [ ] Integration tested
- [ ] Documentation update
<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **Documentation**
- Updated README files to reflect the use of `pnpm` as the recommended
package manager, including installation instructions and best practices.

- **New Features**
- Transitioned scripts in the project to utilize `pnpm` for various
tasks including development, building, and testing.

- **Configuration**
- Modified Playwright configuration and other build configurations to
use `pnpm` for starting the web server and managing dependencies.

- **Dependency Updates**
- Updated Spark dependency version from `3.5.0` to `3.5.1` and Jackson
version from `2.15.1` to `2.15.2`.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

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---------

Co-authored-by: Sean Lynch <[email protected]>
Co-authored-by: ken-zlai <[email protected]>

Author: 3 people

build.sbt

@@ -240,14 +240,14 @@ lazy val frontend = (project in file("frontend"))
     buildFrontend := {
       println("Installing frontend dependencies...")
       import scala.sys.process._
-      val npmCiResult = Process("npm ci", file("frontend")).!
+      val pnpmCiResult = Process("pnpm install --frozen-lockfile", file("frontend")).!
 
-      if (npmCiResult != 0) {
-        sys.error("npm ci failed!")
+      if (pnpmCiResult != 0) {
+        sys.error("pnpm install failed!")
       }
 
       println("Building frontend...")
-      val buildResult = Process("npm run build", file("frontend")).!
+      val buildResult = Process("pnpm run build", file("frontend")).!
 
       if (buildResult == 0) {
         println("Copying frontend assets to /hub/public...")