Add routes and navigation skeleton for the presentation flow

### Description
The presentation flow introduces new screens that don't yet exist in the app. This issue covers wiring up the route structure and navigation guards before any screen-specific work begins.

### Screens to add

| Route | Purpose |
|---|---|
| `/presentation/request` | Proof Request — list of matching credentials |
| `/presentation/details` | Proof Details — claims being shared |
| `/presentation/success` | Presentation sent successfully |

### Acceptance criteria
- [ ] Routes are defined in the router and accessible via navigation
- [ ] All routes are protected (require stored tenant ID), consistent with existing flow
- [ ] A stub page component exists for each route
- [ ] Navigation from `/presentation/request` → `/presentation/details` → `/presentation/success` works end to end with dummy data
- [ ] A back (`<`) button on `/presentation/request` and `/presentation/details` navigates to the previous screen

### Notes
Follow the existing pattern in `src/constants/routes.ts` and `src/pages/`.
OID4VP spec ref: §3.1 (Same Device Flow), §3.2 (Cross Device Flow).