Investigate how to optimize UI initialization

### What is this about?

We should investigate how slow each step of UI initialization is, and make plans to improve overall initialization time.

This would include everything from the start of the execution of `ui.js` to the initial render of the current page.

### Scenario

_No response_

### Design

_No response_

### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

- We have investigated UI initialization performance and written up a report about it
- This could be shared just as a GitHub comment
- Separate issues have been created for each identified opportunity for optimizing performance

### Stakeholder review needed before the work gets merged

- [X] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

_No response_