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/controller/testsuite/test.c

@@ -403,7 +403,7 @@ int cmd_worker(int argc, char* argv[])
 
     active_ctx = &workerctx;
 
-    delaymgr_init(&delaymgr, 2, NULL);
+    delaymgr_init(&delaymgr, 2000 /* precision_ms */, NULL);
     delaymgr_start(&delaymgr);
     delay_task(&delaymgr, 5, -1, (delay_task_entry_fn_t)worker_house_keeping,
                &workerctx);