t-354.2: Update Developer.hs to use dev.md workflow

Update Developer.hs (Telegram orchestrator) to run dev.md workflow instead of calling Coder.runCoderSubagent.

Changes: 1. Replace Coder.runCoderSubagent call with running dev.md workflow via Op 2. Pass task description and namespace as workflow variables 3. Map Op events to Telegram message updates (editMessageText) 4. Keep the async spawn pattern (spawnOrchestrator)

This removes the dependency on Coder.hs.