refactor(background-agent): normalize task ID field naming

Rename BackgroundTask and attempt ID fields to camelCase across background-agent consumers while moving BackgroundManager construction to a single config object.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-openagent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/tools/delegate-task/metadata-await.test.ts

@@ -36,7 +36,7 @@ describe("task tool metadata awaiting", () => {
           prompt: "Do something",
           agent: "explore",
           status: "pending",
-          sessionID: "ses_child",
+          sessionId: "ses_child",
         }),
         getTask: () => undefined,
       },