feat: add config_repl Phase 1 — HEAD-file storage, SHA-256, trim, stale check, sanitise_cn

- config_repl.h/.c: atomic versioned file save, pointer file, trim, stale check
- test_config_repl.c: 17 Unity tests covering all Phase 1 storage functions
- typemap.h: add repl/heartbeat types + union members for xce_request_t/xce_reply_t
- clusterconfig.h: add config_generation field to cluster_config_t (capnp schema ref)
- meson.build: add config_repl.c and test_config_repl.c to build targets
- controller_test.c: register test_config_repl dispatch function

src/controller/meson.build

@@ -1,5 +1,6 @@
 controller_src = [
   'cluster.c',
+  'config_repl.c',
   'dataex.c',
   'ha.c',
   'job.c',
@@ -97,12 +98,16 @@ controller_unit_test_src = [
   'testsuite/test_p3_hardening.c',
   'testsuite/test_p3_manual_failover.c',
   'testsuite/test_ctrl_metrics.c',
+  'testsuite/test_config_repl.c',
   'persist.c',
   'ha.c',
   'repl.c',
   'ctrl_metrics.c',
+  'config_repl.c',
 ]
 
+ssl_dep = dependency('openssl')
+
 controller_unit_test_deps = [
   libxce_dep,
   unity_dep,
@@ -110,6 +115,7 @@ controller_unit_test_deps = [
   thread_dep,
   zlib_dep,
   c_capnproto_dep,
+  ssl_dep,
 ]
 
 controller_unit_test = executable('controller_unit_test',