secure-ntp: remove the chrony pkg NM dispatcher that clobbered the NTS source

NTS was inactive on the clean-build deploy (secure-ntp-d1621e9, comet-beacon-54):
chronyc authdata showed a plain IP source in Mode '-', Cook 0, with no NTS-KE
attempt at all -- chrony was on plain NTP.

Root cause: NetworkManager runs dispatcher scripts from BOTH
/etc/NetworkManager/dispatcher.d and /usr/lib/NetworkManager/dispatcher.d, merged
and sorted by filename. The chrony RPM ships
/usr/lib/NetworkManager/dispatcher.d/20-chrony-dhcp, which writes the DHCP
option-42 server to the SAME /run/chrony-dhcp/<iface>.sources file our
10-chrony-dhcp-ntp uses. Sorting after 10-, it ran last and overwrote our
`server ntp.fleet.lab iburst nts` line with `server 192.168.50.10 iburst`, then
reloaded chrony -- last writer wins on the shared filename, silently defeating
authenticated time.

Isolation proof: removing the distro script + hand-writing the NTS source brought
NTS up immediately (ntp.fleet.lab NTS, Cook 8, zero NAKs), confirming the host
image, the fleet-signed NTS-KE cert, DNS, and tcp/4460 were all already correct --
the collision was the sole defect.

Fix: the provisioner removes /usr/lib/NetworkManager/dispatcher.d/20-chrony-dhcp
at build (our dispatcher supersedes it in both modes); 20-chrony-onoffline is left
in place (harmless). Documents the finding in the dispatcher header,
docs/secure-ntp-design.md, and the CLAUDE.md secure_ntp note. BENCH-VERIFY on the
next clean build: a normal boot reaches NTS/cookies>0 with no manual step.

diskless.pkr.hcl

@@ -448,6 +448,15 @@ build {
       "if [ \"${var.secure_ntp}\" = \"true\" ]; then NTP_MODE=nts; else NTP_MODE=dhcp; fi",
       "sed -i \"s/@NTP_MODE@/$NTP_MODE/; s/@NTP_PREFIX@/${var.ntp_prefix}/\" /etc/NetworkManager/dispatcher.d/10-chrony-dhcp-ntp",
       "restorecon /etc/NetworkManager/dispatcher.d/10-chrony-dhcp-ntp",
+      # Remove the chrony package's OWN NM dispatcher. NetworkManager merges
+      # dispatchers from /etc AND /usr/lib sorted by name, so /usr/lib/.../20-chrony-dhcp
+      # runs AFTER our 10-chrony-dhcp-ntp and writes the DHCP option-42 server to the
+      # SAME /run/chrony-dhcp/<iface>.sources — clobbering our NTS line and silently
+      # defeating authenticated time (bench 2026-07-11, comet-beacon-54: chrony fell
+      # back to plain NTP, authdata Mode '-', Cook 0; removing it → NTS Cook 8). Our
+      # dispatcher supersedes it in BOTH modes, so drop it unconditionally. Leave
+      # 20-chrony-onoffline (only marks sources online/offline — harmless).
+      "rm -f /usr/lib/NetworkManager/dispatcher.d/20-chrony-dhcp",
       "sed -i -E 's/^[[:space:]]*(pool|server)[[:space:]]/#&/' /etc/chrony.conf",
       "grep -q '^sourcedir /run/chrony-dhcp' /etc/chrony.conf || echo 'sourcedir /run/chrony-dhcp' >> /etc/chrony.conf",
       "if [ \"${var.secure_ntp}\" = \"true\" ]; then echo '==> secure NTP: NTS via <${var.ntp_prefix}>.<dhcp-domain> (fleet-CA-authenticated)'; { printf '\\n# Secure NTP (NTS, RFC 8915) — verify the server against the fleet CA. docs/secure-ntp-design.md\\n'; printf 'ntstrustedcerts /etc/dot1x/radius-ca.pem\\n'; printf 'nocerttimecheck 1\\n'; } >> /etc/chrony.conf; else echo '==> legacy NTP: unauthenticated DHCP option-42'; fi",