feat(plugin): name-addressed XRecord CRUD on the HostApi (API v8)

Add create/read/update/delete/list for XRecord objects under
named-object-dictionary paths to the plugin HostApi, with five additive
PluginRequest/PluginResponse variants, dispatch through the shared
handler, in-process HostSession methods and both out-of-process proxies.

- dictionary paths walk from the NOD root; create seeds missing
  dictionaries (ensure_image_dictionary bootstrap) and refuses existing
  names; update refuses missing ones; refusals precede the undo step
- entry group codes validated (1..=369, never 5/105); payload content is
  the plugin's own
- each mutating call is one undo step: the pending history snapshot
  restores the objects map byte-exactly, auto-created dictionaries
  included (tested)
- typed entries survive DWG and DXF write/reload round-trips (tested);
  update drops verbatim raw bytes so saves emit the new content
- bump API_VERSION 7 -> 8 with the build.rs version_info in lockstep,
  mirroring the v7 addition; MIN_SUPPORTED stays 3

crates/ocs_plugin_api/src/ipc/server.rs

@@ -117,5 +117,39 @@ pub fn handle_plugin_request(
             PluginResponse::TableResult(host.table_operation(operation))
         }
         RunCommand { request } => PluginResponse::CommandResult(host.run_command(request)),
+        CreateXRecord {
+            dictionary_path,
+            name,
+            entries,
+        } => {
+            let path: Vec<&str> = dictionary_path.iter().map(String::as_str).collect();
+            PluginResponse::XRecordCreateResult(host.create_xrecord(&path, &name, entries))
+        }
+        ReadXRecord {
+            dictionary_path,
+            name,
+        } => {
+            let path: Vec<&str> = dictionary_path.iter().map(String::as_str).collect();
+            PluginResponse::XRecordEntries(host.read_xrecord(&path, &name))
+        }
+        UpdateXRecord {
+            dictionary_path,
+            name,
+            entries,
+        } => {
+            let path: Vec<&str> = dictionary_path.iter().map(String::as_str).collect();
+            PluginResponse::XRecordUpdateResult(host.update_xrecord(&path, &name, entries))
+        }
+        DeleteXRecord {
+            dictionary_path,
+            name,
+        } => {
+            let path: Vec<&str> = dictionary_path.iter().map(String::as_str).collect();
+            PluginResponse::XRecordDeleteResult(host.delete_xrecord(&path, &name))
+        }
+        ListXRecords { dictionary_path } => {
+            let path: Vec<&str> = dictionary_path.iter().map(String::as_str).collect();
+            PluginResponse::XRecordNames(host.list_xrecords(&path))
+        }
     }
 }