feat(frontend): Upgrade to Next.js v15 + update config (#10042)

- Resolves #10041

Upgrading to Next v15 isn't trivial, but still a good idea if not simply
necessary.

### Changes 🏗️

- Upgrade Next.js from `v14.2.26` to `v15.3.2`
- Fix usage of now-async APIs `params`, `searchParams`, `headers`
([docs](https://nextjs.org/docs/app/guides/upgrading/version-15#async-request-apis-breaking-change))

- Update Next+TypeScript configs
  - Set build target to ES2022 for better performance
  - Unignore TypeScript build errors
  - Set `hideSourceMaps: false` because OSS FTW :)
  - Remove obsolete `webpack.config.js`

- Fix existing warnings/errors
  - Fix Sentry missing navigation hook warning
- Fix `DYNAMIC_SERVER_USAGE` build error on `/profile` and
`/marketplace`
- Moved `getStoreData` to a proper server action `getMarketplaceData`
  - Fix breaking CSS syntax error in `customnode.css`

- Use Turbopack for faster dev+test build times
- Add separate build step to frontend CI workflow: this also fixes the
test timing out if the build takes too long

Other technical improvements:
- Wrap `handleSortChange` in `MarketplaceSearchPage` in `useCallback`
- Fix typing in `ProfileInfoForm`
- Improve output of frontend tests

> [!NOTE]
> Next prints this error (in dev mode):
> ```
> Error: Route "/marketplace" used `cookies().getAll()`. `cookies()`
should be awaited before using its value. Learn more:
https://nextjs.org/docs/messages/sync-dynamic-apis
>     at Object.getAll (src/lib/supabase/getServerSupabase.ts:16:31)
>     at getAll (../../src/cookies.ts:115:41)
> ...
> ```
> As far as I can see, this isn't breaking, and will become a warning in
prod. See also [the Next docs about this
issue](https://nextjs.org/docs/messages/sync-dynamic-apis)

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Follow the full release QA test script

#### For configuration changes:
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

---------

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/platform-frontend-ci.yml

@@ -103,11 +103,15 @@ jobs:
       - name: Setup .env
         run: cp .env.example .env
 
+      - name: Build frontend
+        run: pnpm build --turbo
+        # uses Turbopack, much faster and safe enough for a test pipeline
+
       - name: Install Browser '${{ matrix.browser }}'
         run: pnpm playwright install --with-deps ${{ matrix.browser }}
 
       - name: Run Playwright tests
-        run: pnpm test --project=${{ matrix.browser }}
+        run: pnpm test:no-build --project=${{ matrix.browser }}
 
       - name: Print Final Docker Compose logs
         if: always()