feat(MR-656): inline query strings in CLI and HTTP server

CLI:
- Add -e / --query-string <STRING> to omnigraph read and omnigraph change
- Exactly one of --query, --query-string, --alias is required (3-way XOR)
- Empty --query-string is rejected with a clear error

HTTP:
- New POST /query (read-only, clean field names: query/name/params/branch/snapshot)
- Mutations on /query are rejected with 400 -- use POST /change instead
- ChangeRequest fields polished: query (alias query_source), name (alias query_name)
- POST /read and POST /change remain byte-compatible for existing clients

Tests:
- cli.rs: -e happy-path on read/change, mutex error vs --query, empty -e rejected
- system_local.rs: inline -e read and -e change exercise the local flow
- system_remote.rs: inline -e read/change over HTTP plus direct /query 200/400
- server.rs: /query 200, /query 400 on mutation, /change legacy field alias
- openapi.rs: new /query path, QueryRequest schema, ChangeRequest field-name polish

Docs: cli.md (-e examples), cli-reference.md (read/change rows), server.md (/query)
Co-Authored-By: Ragnor Comerford <ragnor.comerford@gmail.com>

crates/omnigraph-server/examples/bench_actor_isolation.rs

@@ -199,8 +199,8 @@ async fn drive_light_actor(
     let mut other = 0usize;
     for op_idx in 0..ops {
         let request_body = ChangeRequest {
-            query_source: "query insert_person($name: String, $age: I32) {\n    insert Person { name: $name, age: $age }\n}".to_string(),
-            query_name: Some("insert_person".to_string()),
+            query: "query insert_person($name: String, $age: I32) {\n    insert Person { name: $name, age: $age }\n}".to_string(),
+            name: Some("insert_person".to_string()),
             params: Some(serde_json::json!({
                 "name": format!("light-{actor_idx}-{op_idx}"),
                 "age": op_idx as i32,

crates/omnigraph-server/examples/bench_concurrent_http.rs

@@ -121,8 +121,8 @@ async fn drive_actor(
     for op_idx in 0..ops {
         let table_idx = pick_table(actor_idx, op_idx, mode, num_tables);
         let request_body = ChangeRequest {
-            query_source: build_query_source(table_idx),
-            query_name: Some("insert_item".to_string()),
+            query: build_query_source(table_idx),
+            name: Some("insert_item".to_string()),
             params: Some(serde_json::json!({
                 "name": format!("a{actor_idx}_o{op_idx}"),
                 "value": op_idx as i32,