feat: P2.5-5/6 add --peers/--ca-cert parsing to worker+scheduler with validation

Worker (P2.5-5):
- Added parse_peers() static helper to src/worker/src/main.c
- Switched getopt to getopt_long to support --peers and --ca-cert long options
- When --peers is given: parses into xce_cluster_config_t, calls
  xce_cluster_config_validate(), logs INFO with candidate count/identity/ca_cert
- If validation fails: prints clear error and exits(1)
- WARN logged when candidates_count > 3
- Backward compatible: no --peers falls back to existing single-controller path

Scheduler (P2.5-6):
- Added parse_peers() static helper to src/scheduler/src/main.c
- Extended argp struct with --peers (-P) and --ca-cert (-C) options
- Same validation/logging pattern as worker
- Backward compatible: no --peers falls back to existing single-controller path

Tests (new):
- src/lib/testsuite/test_cluster_parse.c: 8 unit tests for parse_peers logic
  (single entry, multiple entries, no-name format, empty/null/missing-port errors,
  name-stripped correctly, MAX_HA_CANDIDATES cap respected)
- Registered in test.c and meson.build
- All 8 tests GREEN; 3 pre-existing failures in unrelated GC/CSE tests unchanged

src/lib/testsuite/test.c

@@ -33,6 +33,7 @@ extern void test_zarray_cow(void);
 extern void test_kvmgr_capture(void);
 extern void test_hooks(void);
 extern void test_cluster(void);
+extern void test_cluster_parse(void);
 
 void setUp(void) { return; }
 
@@ -135,6 +136,7 @@ int main(int argc, char* argv[])
     TEST(test_kvmgr_capture);
     TEST(test_hooks);
     TEST(test_cluster);
+    TEST(test_cluster_parse);
 
     return UNITY_END();
 }