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/features/background-agent/task-poller.ts

@@ -131,7 +131,7 @@ export async function checkAndInterruptStaleTasks(args: {
     if (task.status !== "running") continue
 
     const startedAt = task.startedAt
-    const sessionID = task.sessionID
+    const sessionID = task.sessionId
     if (!startedAt || !sessionID) continue
 
     const sessionStatus = sessionStatuses?.[sessionID]?.type