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/index.ts

@@ -1,7 +1,7 @@
 /**
  * Atlas - Master Orchestrator Agent
  *
- * Orchestrates work via delegate_task() to complete ALL tasks in a todo list until fully done.
+ * Orchestrates work via task() to complete ALL tasks in a todo list until fully done.
  * You are the conductor of a symphony of specialized agents.
  *
  * Routing:
@@ -111,7 +111,7 @@ export function createAtlasAgent(ctx: OrchestratorContext): AgentConfig {
 
   const baseConfig = {
     description:
-      "Orchestrates work via delegate_task() to complete ALL tasks in a todo list until fully done. (Atlas - OhMyOpenCode)",
+      "Orchestrates work via task() to complete ALL tasks in a todo list until fully done. (Atlas - OhMyOpenCode)",
     mode: MODE,
     ...(ctx.model ? { model: ctx.model } : {}),
     temperature: 0.1,