Add route preference endpoints with test coverage

[Copilot]

Implements separate REST endpoints for RoutePreference entities (create, list, delete) with comprehensive test coverage. The existing RoutePreference model, schema, and service were already in place but lacked HTTP endpoints.

Changes

New endpoints at /api/v1/users/route-preferences:

• GET / - List all route preferences for authenticated user
• POST / - Create route preference with prompt and coordinate pairs
• DELETE /{id} - Delete specific route preference

Test coverage (30 new tests):

• Endpoint tests: authentication, authorization, CRUD operations, coordinate validation
• Service tests: business logic, user isolation, data integrity

Example Usage

# Create a route preference
POST /api/v1/users/route-preferences
{
  "prompt": "Prefer trains over buses",
  "from_latitude": 60.1699,
  "from_longitude": 24.9384,
  "to_latitude": 60.2055,
  "to_longitude": 24.6559
}

# Response: 201 Created
{
  "id": 1,
  "prompt": "Prefer trains over buses",
  "from_latitude": 60.1699,
  "from_longitude": 24.9384,
  "to_latitude": 60.2055,
  "to_longitude": 24.6559,
  "created_at": "2025-11-13T14:25:00Z"
}

Follows the same architectural pattern as GlobalPreference endpoints for consistency.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Create new route-specific preference endpoints in the backend</issue_title>
<issue_description>Add separate endpoints (and services) for adding, getting and deleting RoutePreference.</issue_description>

<agent_instructions>Implement tests for this issue.</agent_instructions>

Comments on the Issue (you are @copilot in this section)

• Fixes Create new route-specific preference endpoints in the backend #55

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