Add price prediction and fare trend analytics

[gelluisaac]

Description

    Implement machine learning-based price predictions to help users determine optimal booking times and expected price movements.

    ## Scope
    - packages/backend/src/services/PriceOracleService.ts
    - packages/client/app/search/
    - packages/backend/src/api/routes/analytics.ts

    ## Acceptance Criteria
    - [ ] LSTM model trained on historical fare data
    - [ ] Price prediction displayed for selected routes
    - [ ] Confidence score shown alongside predictions
    - [ ] Fare trend chart shows 30/60/90-day history
    - [ ] Recommendations: buy now or wait indicators
    - [ ] Seasonal pricing patterns identified and displayed
    - [ ] User can enable price drop notifications for watched routes
    - [ ] Model retrained weekly with new data