fix: spurious errors/warnings from a pc13v HA deploy (bug-1872..1877)

- bug-1872 (worker): "Failed to find any disk statistics in
  /proc/diskstats" ERROR every 15 s on an NVMe-only host. The whole-disk
  filter guessed from the name and skipped anything ending in a digit or
  containing 'p' -- every nvmeXnY, mmcblkN, even sdp -- so io was never
  reported. diskstats.h now counts a device only when
  /sys/block/<name>/device exists (real disks; not partitions, loop, dm,
  md, zram), and a host with no disk warns once.
- bug-1873 (worker): "Failed to get worker pid" WARN on job start. MainPID
  reads 0 until systemd has forked the new transient unit; xcecd.c already
  retries, so the miss is DEBUG and the final failure names the unit.
- bug-1874 (scheduler): deprecation WARN for the legacy xce_sched_fcfs on
  every start, though builtin_fcfs is the picker. Registration still wraps
  a job_elect_fn plugin but no longer warns; selecting one warns once.
- bug-1875 (apiserver): "Not running as root -- PAM authentication will not
  work" with the default provider config_file; now only for provider pam.
- bug-1876 (controller): standbys logged "cluster_init_phase2 ... failed
  (rc=-22)" WARN every 3 s while waiting for the primary's config push,
  a state the function itself calls normal. It returns -EAGAIN for that
  wait; callers log it at INFO, other failures still WARN.
- bug-1877 (controller): "WAL/snapshot stored unencrypted" warned without
  looking. persist_path_encrypted() checks fscrypt (statx) and dm-crypt
  (sysfs dm/uuid CRYPT-, through LVM slaves); the warning stays when the
  storage is not shown to be encrypted (e.g. a plain /tmp).

Tests: worker diskstats_test (2 of 4 RED on the old filter with pc13v's
/proc/diskstats), controller test_phase2_cold_boot and
test_persist_encryption, scheduler picker tests, apiserver
TestRootWarning. Full ASAN build: all 113 suites pass (controller 319/0,
harness 141/0).

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/controller/myapp.c

@@ -438,7 +438,13 @@ skip_election:;
              * node already loaded its config from disk pre-election. */
             if (!c.ha.phase2_done) {
                 int prc = cluster_init_phase2(&c);
-                if (prc != 0) {
+                if (ha_phase2_rc_is_waiting(prc)) {
+                    /* bug-1876: the normal cold-boot wait, not a failure */
+                    INFO("myapp_run: standby waiting for the primary's "
+                         "config push before cluster_init_phase2; will "
+                         "retry");
+                    ha_schedule_phase2_retry(&c);
+                } else if (prc != 0) {
                     WARN("myapp_run: cluster_init_phase2 on standby rejoin "
                          "failed (rc=%d) — WAL not recovered; member stays "
                          "alive and will retry (bug-1477: this passive "