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/unstable-agent-timeout.test.ts

@@ -22,8 +22,8 @@ describe("executeUnstableAgentTask timeout handling", () => {
     const { executeUnstableAgentTask } = require("./unstable-agent-task")
 
     const mockManager = {
-      launch: async () => ({ id: "task_001", sessionID: "ses_timeout", status: "running" }),
-      getTask: () => ({ id: "task_001", sessionID: "ses_timeout", status: "running" }),
+      launch: async () => ({ id: "task_001", sessionId: "ses_timeout", status: "running" }),
+      getTask: () => ({ id: "task_001", sessionId: "ses_timeout", status: "running" }),
     }
 
     const mockClient = {