Audit / call log should be opt-out not opt-in

[arizen-dev]

Per Social's Reddit feedback (Signal 1 from r/ClaudeAI + r/Codex):

Users want to see what's being offloaded. v0.5 implements a call log via DEEPSEEK_MCP_LOG=1 but it's opt-in. Consider making it always-on (log to ~/.deepseek-mcp/calls.jsonl).

Comments:

• r/ClaudeAI: 'without the log i would have missed it'
• r/Codex: 'log every offload with input size, model, latency, and cost'

For v0.5 review: decide default behavior.