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/tasks-todowrite-disabler/constants.ts

@@ -16,7 +16,7 @@ export const REPLACEMENT_MESSAGE = `TodoRead/TodoWrite are DISABLED because expe
 3. DO THE WORK
 4. TaskUpdate({ id: "T-xxx", status: "completed" })
 
-CRITICAL: 1 task = 1 delegate_task. Fire independent tasks concurrently.
+CRITICAL: 1 task = 1 task. Fire independent tasks concurrently.
 
 **STOP! DO NOT START WORKING DIRECTLY - NO MATTER HOW SMALL THE TASK!**
 Even if the task seems trivial (1 line fix, simple edit, quick change), you MUST: