server: group routes by category and purpose (#9270)

The route assembly in Handler lacked clear organization making it
difficult scan for routes and their relationships to each other. This
commit aims to fix that by reordering the assembly of routes to group
them by category and purpose.

Also, be more specific about what "config" refers to (it is about CORS
if you were wondering... I was.)

envconfig/config_test.go

@@ -134,7 +134,7 @@ func TestOrigins(t *testing.T) {
 		t.Run(tt.value, func(t *testing.T) {
 			t.Setenv("OLLAMA_ORIGINS", tt.value)
 
-			if diff := cmp.Diff(Origins(), tt.expect); diff != "" {
+			if diff := cmp.Diff(AllowedOrigins(), tt.expect); diff != "" {
 				t.Errorf("%s: mismatch (-want +got):\n%s", tt.value, diff)
 			}
 		})