Fix compilation errors for non-test builds

Fixed build errors in tinydfs_server and example_client targets caused
by missing timeout parameter and simulation client references.

**Changes:**

**main_server.c:**
- Added int timeout variable declaration in metadata_server_main()
- Added int timeout variable declaration in chunk_server_main()
- Pass &timeout to metadata_server_init() call
- Pass &timeout to metadata_server_step() call
- Pass &timeout to chunk_server_init() call
- Pass &timeout to chunk_server_step() call

**system.c:**
- Guarded simulation_client.h include with #ifdef BUILD_TEST
- Guarded PROCESS_TYPE_CLIENT enum value with #ifdef BUILD_TEST
- Guarded SimulationClient member in Process union with #ifdef BUILD_TEST
- Guarded is_client() function with #ifdef BUILD_TEST
- Guarded client detection logic in spawn_simulated_process()
- Guarded PROCESS_TYPE_CLIENT cases in all switch statements:
  - spawn_simulated_process() init switch
  - free_process() cleanup switch
  - update_simulation() step switch

**Result:**
- tinydfs_server.out now compiles successfully
- example_client.out now compiles successfully
- tinydfs_test.out continues to work correctly
- Simulation client code only included when BUILD_TEST is defined
- All three build targets pass compilation with only pre-existing warnings

The simulation_client code is now properly isolated to test builds only,
preventing linker errors when building the real server and example client.

src/system.c

@@ -5,7 +5,9 @@
 #include "system.h"
 #include "chunk_server.h"
 #include "metadata_server.h"
+#ifdef BUILD_TEST
 #include "simulation_client.h"
+#endif
 
 #ifdef _WIN32
 #define NATIVE_HANDLE HANDLE
@@ -135,7 +137,9 @@ typedef struct {
 typedef enum {
     PROCESS_TYPE_METADATA_SERVER,
     PROCESS_TYPE_CHUNK_SERVER,
+#ifdef BUILD_TEST
     PROCESS_TYPE_CLIENT,
+#endif
 } ProcessType;
 
 struct Process {
@@ -152,7 +156,9 @@ struct Process {
     union {
         ChunkServer      chunk_server;
         MetadataServer   metadata_server;
+#ifdef BUILD_TEST
         SimulationClient simulation_client;
+#endif
     };
 };
 
@@ -244,6 +250,7 @@ static bool is_leader(int argc, char **argv)
     return false;
 }
 
+#ifdef BUILD_TEST
 static bool is_client(int argc, char **argv)
 {
     for (int i = 0; i < argc; i++)
@@ -251,6 +258,7 @@ static bool is_client(int argc, char **argv)
             return true;
     return false;
 }
+#endif
 
 #define MAX_ARGS 128
 
@@ -299,16 +307,21 @@ int spawn_simulated_process(char *args)
     }
 
     bool leader = is_leader(argc, argv);
+#ifdef BUILD_TEST
     bool client = is_client(argc, argv);
+#endif
 
     Process *process = malloc(sizeof(Process));
     if (process == NULL)
         return -1;
 
     // Determine process type
+#ifdef BUILD_TEST
     if (client) {
         process->type = PROCESS_TYPE_CLIENT;
-    } else if (leader) {
+    } else
+#endif
+    if (leader) {
         process->type = PROCESS_TYPE_METADATA_SERVER;
     } else {
         process->type = PROCESS_TYPE_CHUNK_SERVER;
@@ -334,9 +347,11 @@ int spawn_simulated_process(char *args)
         case PROCESS_TYPE_CHUNK_SERVER:
             num_polled = chunk_server_init(&process->chunk_server, argc, argv, contexts, polled, &timeout);
             break;
+#ifdef BUILD_TEST
         case PROCESS_TYPE_CLIENT:
             num_polled = simulation_client_init(&process->simulation_client, argc, argv, contexts, polled, &timeout);
             break;
+#endif
         default:
             num_polled = -1;
             break;
@@ -368,9 +383,11 @@ static void free_process(Process *process)
         case PROCESS_TYPE_CHUNK_SERVER:
             chunk_server_free(&process->chunk_server);
             break;
+#ifdef BUILD_TEST
         case PROCESS_TYPE_CLIENT:
             simulation_client_free(&process->simulation_client);
             break;
+#endif
     }
     free(process);
 }
@@ -553,9 +570,11 @@ void update_simulation(void)
             case PROCESS_TYPE_CHUNK_SERVER:
                 num_polled = chunk_server_step(&current_process->chunk_server, contexts, polled, num_polled, &timeout);
                 break;
+#ifdef BUILD_TEST
             case PROCESS_TYPE_CLIENT:
                 num_polled = simulation_client_step(&current_process->simulation_client, contexts, polled, num_polled, &timeout);
                 break;
+#endif
         }
 
         if (num_polled < 0) {