Add cost tracking and $0.01/day cap to goose-proxy

[BryanChasko]

Agent Task

Agent: ellow-gander-mechanic
Depends on: none
Branch: feat/proxy-cost-cap
Source: specs/marvel-snap-pipeline/tasks.md

Acceptance Criteria

• Track cumulative daily cost per model via Valkey
• Reset counter at midnight
• Reject calls when daily cap exceeded
• Cap configurable via SNAP_DAILY_COST_CAP env var, default $0.01

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Generated from specs/marvel-snap-pipeline/tasks.md by generate-task-issues.py