[BUG]: App fails to build missing SupportOpenSource page and duplicate routes in App.tsx

## Bug Description

### Bug 1 — Missing SupportOpenSource page (build breaking)
App.tsx imports ./Pages/SupportOpenSource and defines a route for
/support-debateai, but the file does not exist in the codebase.
This causes an immediate Vite build error on startup:

"Failed to resolve import './Pages/SupportOpenSource' from 'src/App.tsx'.
Does the file exist?"

The app cannot load at all until this is resolved.

### Bug 2 — Duplicate routes
The following routes are defined twice in App.tsx:
- /coach
- coach/strengthen-argument

## Steps to Reproduce
1. Clone the repo
2. cd frontend && npm run dev
3. App immediately fails with the import error above

## Expected Behaviour
- App builds and runs without errors
- /support-debateai renders a valid page
- Each route is defined only once

## Files Affected
- frontend/src/App.tsx
- frontend/src/Pages/SupportOpenSource.tsx (missing)

##Screenshots:

### Steps to Reproduce

_No response_

### Logs and Screenshots

_No response_

### Environment Details

_No response_

### Impact

Critical - Application is unusable

### Code of Conduct

- [x] I have joined the [Discord server](https://discord.gg/hjUhu33uAn) and will post updates there
- [x] I have searched existing issues to avoid duplicates