Token budget & cost tracking: per-session usage, gc costs command, budget circuit breaker

[alexsiri7]

Add comprehensive token budget management to Gas City:

• gc costs command with daily/weekly digest summaries
• Per-session token usage tracking via Stop hook persistence
• OTel token usage counters per agent/model
• Token budget circuit breaker that stops agents when budget exhausted
• Adaptive pool sizing based on remaining token budget
• Per-role max_session_tokens cap with session kill on exceed
• Token exhaustion detection step in deacon patrol formula
• Agent runtime and token economy monitoring in patrol formulas

This enables operators to monitor and control token spend across all agents, with automatic budget enforcement.