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-cli/tests/system_local.rs

@@ -246,6 +246,37 @@ fn local_cli_end_to_end_init_load_read_change_read_flow() {
     ));
     assert_eq!(read_after["row_count"], 1);
     assert_eq!(read_after["rows"][0]["p.name"], "Eve");
+
+    // Inline-source variants of the same read/change flow (CLI `-e` /
+    // `--query-string`). Confirms that file-less invocations reach the
+    // engine identically, including param binding and `branch=main` defaults.
+    let inline_change = parse_stdout_json(&output_success(
+        cli()
+            .arg("change")
+            .arg(repo.path())
+            .arg("-e")
+            .arg("query add($name: String, $age: I32) { insert Person { name: $name, age: $age } }")
+            .arg("--params")
+            .arg(r#"{"name":"Inline","age":42}"#)
+            .arg("--json"),
+    ));
+    assert_eq!(inline_change["branch"], "main");
+    assert_eq!(inline_change["query_name"], "add");
+    assert_eq!(inline_change["affected_nodes"], 1);
+
+    let inline_read = parse_stdout_json(&output_success(
+        cli()
+            .arg("read")
+            .arg(repo.path())
+            .arg("--query-string")
+            .arg("query find($name: String) { match { $p: Person { name: $name } } return { $p.name, $p.age } }")
+            .arg("--params")
+            .arg(r#"{"name":"Inline"}"#)
+            .arg("--json"),
+    ));
+    assert_eq!(inline_read["row_count"], 1);
+    assert_eq!(inline_read["rows"][0]["p.name"], "Inline");
+    assert_eq!(inline_read["rows"][0]["p.age"], 42);
 }
 
 #[test]