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/tools/delegate-task/constants.ts

@@ -459,13 +459,13 @@ YOU MUST END YOUR RESPONSE WITH THIS SECTION.
 
 1. **Wave 1**: Fire these tasks IN PARALLEL (no dependencies)
    \`\`\`
-   delegate_task(category="...", load_skills=[...], run_in_background=false, prompt="Task 1: ...")
-   delegate_task(category="...", load_skills=[...], run_in_background=false, prompt="Task N: ...")
+   task(category="...", load_skills=[...], run_in_background=false, prompt="Task 1: ...")
+   task(category="...", load_skills=[...], run_in_background=false, prompt="Task N: ...")
    \`\`\`
 
 2. **Wave 2**: After Wave 1 completes, fire next wave IN PARALLEL
    \`\`\`
-   delegate_task(category="...", load_skills=[...], run_in_background=false, prompt="Task 2: ...")
+   task(category="...", load_skills=[...], run_in_background=false, prompt="Task 2: ...")
    \`\`\`
 
 3. Continue until all waves complete
@@ -476,7 +476,7 @@ YOU MUST END YOUR RESPONSE WITH THIS SECTION.
 WHY THIS FORMAT IS MANDATORY:
 - Caller can directly copy TODO items
 - Wave grouping enables parallel execution
-- Each task has clear delegate_task parameters
+- Each task has clear task parameters
 - QA criteria ensure verifiable completion
 </FINAL_OUTPUT_FOR_CALLER>