fix(async-tasks): inject completed tasks in prompt() for auto-wakeup

[randomm]

Fixes #194

Root Cause

enableAutoWakeup() called SessionPrompt.prompt({ parts: [] }) with empty parts. Completed task results were never injected because prompt-async.ts helper functions were dead code (never imported).

Fix

• Inject completed tasks directly in prompt.ts before message creation
• Delete dead code prompt-async.ts
• Add missing criticalCode markers to manifest: enableAutoWakeup, triggerWakeup, autoWakeupSubscribers, hasUndeliveredCompletedTasks, getAndClearCompletedTasks

Tests

• Type check: ✅ 0 errors
• Tasks test: ✅ 24/24
• Session tests: ✅ 113/113
• Fork verify: ✅ 92/92