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/delegate-task-retry/index.test.ts

@@ -8,7 +8,7 @@ import {
 describe("sisyphus-task-retry", () => {
   describe("DELEGATE_TASK_ERROR_PATTERNS", () => {
     // given error patterns are defined
-    // then should include all known delegate_task error types
+    // then should include all known task error types
     it("should contain all known error patterns", () => {
       expect(DELEGATE_TASK_ERROR_PATTERNS.length).toBeGreaterThan(5)