LF-4722b Fix start:prod path to match container structure

[kathyavini]

Description

This is the follow-up to the PR and the solution was tested live (successfully) during tech daily Feb 6

• LF-4722 Backend container crashes due to missing server.js file #3682

When merging that PR we saw that the /dist folder was successfully built within the container image. The issue was that tsc copies the directory structure of its source, and in the Docker image the path has been set up as /app/src/server.js instead of api/src/server.js. This PR just changes the start:prod script path to match this.

As a side effect you cannot use npm run start:prod locally after this change but as it was meant to be used in hosted container I don't see this as an issue.

@Duncan-Brain I did not delete the npm run start script here because it is used by the Cypress tests.

Jira link: https://lite-farm.atlassian.net/browse/LF-4722

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

• Passes test case
• UI components visually reviewed on desktop view
• UI components visually reviewed on mobile view
• Other (please explain)

We have already tested the change on the droplet directly and it worked to get the backend container up and running again.

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The precommit and linting ran successfully
• I have added or updated language tags for text that's part of the UI
• I have added "MISSING" for all new language tags to languages I don't speak
• I have added the GNU General Public License to all new files