refactor(handler,server): disable SubmitApplication endpoint, replaced by POST /tasks

- Comment out SubmitApplication handler method

- Comment out route registration in server.go (interface + router + placeholder)

- Comment out related handler tests

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/server/server_test.go

@@ -32,7 +32,7 @@ func TestAllRoutesRegistered(t *testing.T) {
 		{"GET", "/api/v1/applications/:id"},
 		{"PUT", "/api/v1/applications/:id"},
 		{"DELETE", "/api/v1/applications/:id"},
-		{"POST", "/api/v1/applications/:id/submit"},
+		// {"POST", "/api/v1/applications/:id/submit"}, // [已禁用] 已被 POST /tasks 取代
 	}
 
 	routeMap := map[string]bool{}