Stream Amp logs to Agent status bar

Update Omni/Agent/Worker.hs to spawn a background thread that tails '_/llm/amp.log' while the Amp agent is running. For each new line in the log: 1. Parse it (it's JSON). 2. Extract a user-friendly summary (e.g. 'Thinking...', 'Tool: Bash'). 3. Update the status bar activity line (AgentLog.updateActivity) with this summary. This provides real-time visibility into what the agent is doing.