Untitled

<Plan>
Now I have all the design guidelines and codebase structure. Let me build the Car Negotiation Calculator app with:

**Backend (server.py):**
1. Models: CarNegotiation (car details, calculated values)
2. Endpoints:
   - POST /api/calculate - Calculate counter-offer based on car details
   - POST /api/negotiations - Save a negotiation scenario
   - GET /api/negotiations - Get saved negotiations
   - DELETE /api/negotiations/{id} - Delete a negotiation

**Frontend:**
1. Main calculator form with car inputs (make, model, year, asking price, mileage, condition)
2. Counter-offer display with Signal Red styling
3. Negotiation tips section
4. Saved negotiations list
5. Swiss/Brutalist design with Chivo + IBM Plex Sans fonts

**Design Elements (from guidelines):**
- Light theme with #FAFAFA background, #E11D48 accent
- Brutalist buttons with shadow-[4px_4px_0px_0px_#000000]
- rounded-none everywhere
- IBM Plex Mono for numbers
- Counter-offer in massive text-5xl/6xl Signal Red
</Plan>

Let me build the complete app now:
Action: $ cd /app/frontend && yarn add @phosphor-icons/react
Observation: yarn add v1.22.22
[1/4] Resolving packages...
[2/4] Fetching packages...
[3/4] Linking dependencies...
[4/4] Building fresh packages...
success Saved lockfile.
success Saved 1 new dependency.
info Direct dependencies
└─ @phosphor-icons/[email protected]
info All dependencies
└─ @phosphor-icons/[email protected]
Done in 53.91s.
[stderr] warning " > [email protected]" has incorrect peer dependency "date-fns@^2.28.0 || ^3.0.0".
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warning "react-scripts > react-dev-utils > [email protected]" has unmet peer dependency "typescript@>= 2.7".
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warning " > [email protected]" has unmet peer dependency "react-is@^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0".
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warning "@craco/craco > cosmiconfig-typescript-loader > [email protected]" has unmet peer dependency "typescript@>=2.7".
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Exit code: 0