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/cli.rs

@@ -1422,6 +1422,102 @@ fn read_requires_name_for_multi_query_files() {
     assert!(stderr.contains("multiple queries"));
 }
 
+#[test]
+fn read_supports_inline_query_string() {
+    let temp = tempdir().unwrap();
+    let repo = repo_path(temp.path());
+    init_repo(&repo);
+    load_fixture(&repo);
+
+    let output = output_success(
+        cli()
+            .arg("read")
+            .arg(&repo)
+            .arg("-e")
+            .arg("query find($name: String) { match { $p: Person { name: $name } } return { $p.name, $p.age } }")
+            .arg("--params")
+            .arg(r#"{"name":"Alice"}"#)
+            .arg("--json"),
+    );
+    let payload: Value = serde_json::from_slice(&output.stdout).unwrap();
+    assert_eq!(payload["query_name"], "find");
+    assert_eq!(payload["row_count"], 1);
+    assert_eq!(payload["rows"][0]["p.name"], "Alice");
+}
+
+#[test]
+fn change_supports_inline_query_string() {
+    let temp = tempdir().unwrap();
+    let repo = repo_path(temp.path());
+    init_repo(&repo);
+    load_fixture(&repo);
+
+    let output = output_success(
+        cli()
+            .arg("change")
+            .arg(&repo)
+            .arg("--query-string")
+            .arg("query add($name: String, $age: I32) { insert Person { name: $name, age: $age } }")
+            .arg("--params")
+            .arg(r#"{"name":"Inline","age":42}"#)
+            .arg("--json"),
+    );
+    let payload: Value = serde_json::from_slice(&output.stdout).unwrap();
+    assert_eq!(payload["query_name"], "add");
+    assert_eq!(payload["affected_nodes"], 1);
+
+    let verify = output_success(
+        cli()
+            .arg("read")
+            .arg(&repo)
+            .arg("-e")
+            .arg("query find($name: String) { match { $p: Person { name: $name } } return { $p.name } }")
+            .arg("--params")
+            .arg(r#"{"name":"Inline"}"#)
+            .arg("--json"),
+    );
+    let verify_payload: Value = serde_json::from_slice(&verify.stdout).unwrap();
+    assert_eq!(verify_payload["row_count"], 1);
+}
+
+#[test]
+fn read_rejects_query_string_combined_with_query() {
+    let temp = tempdir().unwrap();
+    let repo = repo_path(temp.path());
+    init_repo(&repo);
+    load_fixture(&repo);
+
+    let output = output_failure(
+        cli()
+            .arg("read")
+            .arg(&repo)
+            .arg("--query")
+            .arg(fixture("test.gq"))
+            .arg("-e")
+            .arg("query whatever() { match { $p: Person } return { $p.name } }"),
+    );
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    assert!(
+        stderr.contains("cannot be used") || stderr.contains("conflict"),
+        "expected clap conflict error, got: {stderr}"
+    );
+}
+
+#[test]
+fn read_rejects_empty_query_string() {
+    let temp = tempdir().unwrap();
+    let repo = repo_path(temp.path());
+    init_repo(&repo);
+    load_fixture(&repo);
+
+    let output = output_failure(cli().arg("read").arg(&repo).arg("-e").arg(""));
+    let stderr = String::from_utf8(output.stderr).unwrap();
+    assert!(
+        stderr.contains("must not be empty"),
+        "expected empty-string rejection, got: {stderr}"
+    );
+}
+
 #[test]
 fn branch_create_json_outputs_source_and_name() {
     let temp = tempdir().unwrap();