feat(ha-config-bootstrap): implement --vcpus CLI, wire validation, remove vcpus from config (task 2.2)

- Add --vcpus N argp option in main.c; store in myconf.vcpus
- Replace inline argp guard with validate_vcpus() call (returns -EINVAL for <=0)
- Add validate_startup_config() in startup_validation.c: returns 0; writes
  deprecation warning into caller-supplied warn_buf when vcpus key present
- Wire validate_startup_config() into myapp_run() after conffile resolved;
  emit WARN() if warn_buf non-empty (Req 4.4)
- Remove vcpus field from cluster_config_t (clusterconfig.h)
- Preserve capnp ordinal: vcpus @7 -> vcpusDeprecated @7: Void in controller.capnp
- vtaskmgr_init uses only myconf->vcpus with hardcoded default 8
- Add stub C types in typemap.h for capnp schema extensions from task 1.1
- 96 tests pass

src/schema/controller.capnp

@@ -680,7 +680,7 @@ struct ClusterConfig $C.mapname("cluster_config_t") {
   inactiveHeartbeatCount @4: UInt32 $C.mapname("inactive_heartbeat_count");
   fetchJobInterval       @5: UInt32 $C.mapname("fetch_job_interval");
   netioTimeout           @6: UInt32 $C.mapname("netio_timeout");
-  vcpus                  @7: UInt32 $C.mapname("vcpus");
+  vcpusDeprecated        @7: Void;  # removed — use --vcpus CLI flag instead
   resources              @8: List(Resource) $C.mapname("resources") $C.maplistcount("nres");
   queues                 @9: List(QueueConf) $C.mapname("queues") $C.maplistcount("nqueues");
   ugroups                @10: List(GroupConfig) $C.mapname("ugroups") $C.maplistcount("nugroups");