feat: rename delaymgr precision→precision_ms, replace sleep() with nanosleep() (P0-2b)

- Rename `precision` field to `precision_ms` in delaymgr_t struct (delay.h)
- Replace `sleep(mgr->precision)` with `nanosleep()` for 10ms granularity (delay.c)
- Add `#include <time.h>` to delay.c (already in delay.h)
- Update delaymgr_init() to store precision_ms parameter
- Update all call sites: cluster.c (2→200ms), controller/testsuite/test.c (2→2000ms),
  lib/testsuite/test_delay.c (1→1000ms)
- Add TDD test test_delaymgr_precision_ms_field verifying field exists and stores correctly
- delay_task() delay parameter remains in seconds; only sleep granularity changes

src/lib/delay.c

@@ -3,6 +3,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <time.h>
 
 #include "delay.h"
 #include "utils.h"
@@ -17,7 +18,10 @@ static void* delay_worker(void* args)
         time_t        now;
 
         pthread_testcancel();
-        sleep(mgr->precision);
+        {
+            struct timespec ts = { 0, (long)mgr->precision_ms * 1000000L };
+            nanosleep(&ts, NULL);
+        }
 
         it = ordq_peek(&(mgr->tasks), NULL);
         if (it == NULL) {
@@ -100,7 +104,7 @@ int delaymgr_init(delaymgr_t* mgr, int precision, task_run_fn_t runner_fn)
         runner_fn = default_runner_fn;
     }
 
-    mgr->precision = precision;
+    mgr->precision_ms = precision;
     mgr->running   = 0;
     mgr->runner_fn = runner_fn;
     mgr->worker    = 0;