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/config/schema.ts

@@ -12,6 +12,7 @@ const AgentPermissionSchema = z.object({
   edit: PermissionValue.optional(),
   bash: BashPermission.optional(),
   webfetch: PermissionValue.optional(),
+  task: PermissionValue.optional(),
   doom_loop: PermissionValue.optional(),
   external_directory: PermissionValue.optional(),
 })
@@ -183,7 +184,7 @@ export const SisyphusAgentConfigSchema = z.object({
 })
 
 export const CategoryConfigSchema = z.object({
-  /** Human-readable description of the category's purpose. Shown in delegate_task prompt. */
+  /** Human-readable description of the category's purpose. Shown in task prompt. */
   description: z.string().optional(),
   model: z.string().optional(),
   variant: z.string().optional(),