fix: resolve category delegation and command routing with display name agent keys

Category-based delegation (task(category='quick')) was broken because
SISYPHUS_JUNIOR_AGENT sent 'sisyphus-junior' to session.prompt but
config.agent keys are now display names ('Sisyphus-Junior').

- Use getAgentDisplayName() for SISYPHUS_JUNIOR_AGENT constant
- Replace hardcoded 'sisyphus-junior' strings in tools.ts with constant
- Update background-output local constants to use display names
- Add remapCommandAgentFields() to translate command agent fields
- Add raw-key fallback in tool-config-handler agentByKey()

src/tools/background-task/modules/background-output.ts

@@ -8,7 +8,9 @@ import { storeToolMetadata } from "../../../features/tool-metadata-store"
 import type { BackgroundTask } from "../../../features/background-agent"
 import type { ToolContextWithMetadata } from "./utils"
 
-const SISYPHUS_JUNIOR_AGENT = "sisyphus-junior"
+import { getAgentDisplayName } from "../../../shared/agent-display-names"
+
+const SISYPHUS_JUNIOR_AGENT = getAgentDisplayName("sisyphus-junior")
 
 type ToolContextWithCallId = ToolContextWithMetadata & {
   callID?: string