feat: implement API versioning /api/v1/

- All backend routers moved to /api/v1/ prefix
- Frontend BASE_URL updated to /api/v1
- Setup redirect middleware updated to redirect to /api/v1/setup
- Health router path fixed: prefix=/api/v1/health, @router.get('')
- conftest.py: set server_status=online for test fixture
- Created Docs/API_VERSIONING.md with deprecation policy
- Updated Docs/Backend-Development.md with versioning section
- Updated Instructions.md curl examples

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/tests/test_correlation_middleware.py

@@ -27,7 +27,7 @@ def test_correlation_middleware_generates_uuid_when_header_absent() -> None:
 
     # Test with TestClient (synchronous)
     client = TestClient(app)
-    response = client.get("/api/health")
+    response = client.get("/api/v1/health")
 
     # Should have correlation ID header in response
     assert "X-Correlation-ID" in response.headers
@@ -53,7 +53,7 @@ def test_correlation_middleware_preserves_header_from_request() -> None:
 
     client = TestClient(app)
     test_correlation_id = "550e8400-e29b-41d4-a716-446655440000"
-    response = client.get("/api/health", headers={"X-Correlation-ID": test_correlation_id})
+    response = client.get("/api/v1/health", headers={"X-Correlation-ID": test_correlation_id})
 
     # Should return the same correlation ID in response
     assert response.headers["X-Correlation-ID"] == test_correlation_id
@@ -76,7 +76,7 @@ def test_correlation_middleware_stores_in_request_state() -> None:
 
     # Make a request and verify correlation ID is available to handlers
     test_correlation_id = "550e8400-e29b-41d4-a716-446655440000"
-    response = client.get("/api/health", headers={"X-Correlation-ID": test_correlation_id})
+    response = client.get("/api/v1/health", headers={"X-Correlation-ID": test_correlation_id})
 
     # The health endpoint should return 200, proving the correlation ID was processed
     assert response.status_code == 200
@@ -100,11 +100,11 @@ def test_correlation_id_in_response_headers() -> None:
     client = TestClient(app)
 
     # Test without providing header (should generate one)
-    response = client.get("/api/health")
+    response = client.get("/api/v1/health")
     assert "X-Correlation-ID" in response.headers
 
     # Test with providing header (should preserve it)
     test_id = "test-correlation-id-12345"
-    response = client.get("/api/health", headers={"X-Correlation-ID": test_id})
+    response = client.get("/api/v1/health", headers={"X-Correlation-ID": test_id})
     assert response.headers["X-Correlation-ID"] == test_id