refactor: migrate delegate_task to task tool with metadata fixes

- Rename delegate_task tool to task across codebase (100 files)
- Update model references: claude-opus-4-6 → 4-5, gpt-5.3-codex → 5.2-codex
- Add tool-metadata-store to restore metadata overwritten by fromPlugin()
- Add session ID polling for BackgroundManager task sessions
- Await async ctx.metadata() calls in tool executors
- Add ses_ prefix guard to getMessageDir for performance
- Harden BackgroundManager with idle deferral and error handling
- Fix duplicate task key in sisyphus-junior test object literals
- Fix unawaited showOutputToUser in ast_grep_replace
- Fix background=true → run_in_background=true in ultrawork prompt
- Fix duplicate task/task references in docs and comments

src/hooks/empty-task-response-detector.ts

@@ -15,7 +15,7 @@ export function createEmptyTaskResponseDetectorHook(_ctx: PluginInput) {
       input: { tool: string; sessionID: string; callID: string },
       output: { title: string; output: string; metadata: unknown }
     ) => {
-      if (input.tool !== "Task") return
+      if (input.tool !== "Task" && input.tool !== "task") return
 
       const responseText = output.output?.trim() ?? ""