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/include/delay.h

@@ -23,7 +23,7 @@ typedef struct {
 typedef struct {
     pthread_t     worker;
     int           running;
-    int           precision;
+    int           precision_ms;
     task_run_fn_t runner_fn;
     timer_t       timerid;
     ordq_t        tasks;