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/agents/atlas/utils.ts

@@ -47,7 +47,7 @@ Categories spawn \`Sisyphus-Junior-{category}\` with optimized settings:
 ${categoryRows.join("\n")}
 
 \`\`\`typescript
-delegate_task(category="[category-name]", load_skills=[...], run_in_background=false, prompt="...")
+task(category="[category-name]", load_skills=[...], run_in_background=false, prompt="...")
 \`\`\``
 }
 
@@ -105,7 +105,7 @@ Read each skill's description and ask: "Does this skill's domain overlap with my
 
 **Usage:**
 \`\`\`typescript
-delegate_task(category="[category]", load_skills=["skill-1", "skill-2"], run_in_background=false, prompt="...")
+task(category="[category]", load_skills=["skill-1", "skill-2"], run_in_background=false, prompt="...")
 \`\`\`
 
 **IMPORTANT:**