[API] Add API Versioning

[fentz26]

Problem

No API versioning exists. This causes:

• Breaking changes affect all clients
• No deprecation path
• Difficult upgrade experience

Current State

GET /tasks
POST /tasks/{id}/run

Proposed Solution

GET /v1/tasks
POST /v1/tasks/{id}/run

Implementation

func SetupRoutes(mux *http.ServeMux) {
    // API v1
    v1 := http.NewServeMux()
    v1.HandleFunc("/tasks", handleTasks)
    v1.HandleFunc("/tasks/{id}", handleTask)
    // ...
    
    mux.Handle("/v1/", http.StripPrefix("/v1", v1))
    
    // Future: API v2
    // mux.Handle("/v2/", http.StripPrefix("/v2", v2))
}

Acceptance Criteria

• All endpoints prefixed with /v1/
• Old endpoints redirect with deprecation warning
• API version in response headers
• Documentation includes version
• Migration guide for existing clients

Versioning Policy

Change Type	Version Impact
New endpoint	Minor (1.x)
New optional field	Minor (1.x)
Breaking change	Major (2.0)
Bug fix	Patch (1.0.x)

References

• Evaluation Report Section: 1.1 API Design Quality