feat: add safe replay risk dashboard

[FeeeeelixWong]

Summary

• make credential-free replay the default startup path with deterministic BLOCK, WATCH, and PASS fixtures
• surface decision evidence directly in the dashboard and distinguish replay eligibility from executable trading
• require explicit live-mode gates, remove observation-mode wallet requirements, and stop killing unrelated processes when the dashboard port is busy
• refresh the README and add replay-mode coverage

Verification

• Extracted 2414 lines -> /tmp/meme-scanner-final.py
• replay dashboard exercised locally in desktop and mobile viewports