Harden kea socket dir to 0750 in the rendered entrypoints

After v0.1.1 moved the socket dir to /var/run/kea, kea-dhcp4 and
kea-ctrl-agent still crash-loop:

  DHCP4_PARSER_COMMIT_FAIL ... 'socket-name' is invalid: socket path:/var/run/kea
  does not exist or has more relaxed permissions than 750

Kea 2.6+ refuses a unix-socket directory whose mode is more relaxed than
0750. The shared emptyDir is mounted at /var/run/kea with the default 0777,
so kea rejects it. The kea containers run as root, so the entrypoints can
tighten it.

- chmod 0750 the RunDir in both rendered entrypoints after mkdir.
- Assert both entrypoints chmod the socket dir to 0750.

Needs a v0.1.2 release so argocd-apps can bump the operator image.

Claude-Session: https://claude.ai/code/session_01JUoARVdmhxKQHyyyp1pxeT

internal/kea/agent.go

@@ -35,6 +35,7 @@ func EntrypointDHCP4() string {
 set -e
 ORD="${HOSTNAME##*-}"
 mkdir -p %[1]s
+chmod 0750 %[1]s
 sed "s/%[2]s/server${ORD}/g" %[3]s/kea-dhcp4.conf > %[4]s
 exec %[5]s -c %[4]s
 `, RunDir, ThisServerPlaceholder, ConfigDir, DHCP4ConfPath, DHCP4Bin)
@@ -45,6 +46,7 @@ func EntrypointCtrlAgent() string {
 	return fmt.Sprintf(`#!/bin/sh
 set -e
 mkdir -p %[1]s
+chmod 0750 %[1]s
 cp %[2]s/kea-ctrl-agent.conf %[3]s
 exec %[4]s -c %[3]s
 `, RunDir, ConfigDir, CtrlAgentConfPath, CtrlAgentBin)