Add RBAC safeguards and live vault metrics

[Fury03]

Implements the four assigned Phase 3 dashboard issues:

• Gate role actions on the connected caller's Admin permission.
• Require a security checklist acknowledgment before granting SuperAdmin.
• Export role assignments and recent contract events as timestamped CSV or JSON.
• Refresh vault metrics every 30 seconds, format base units, show loading/error states, and enforce preview-based minimum outputs on deposits and withdrawals.

Validation: React tests (282 passed), React build, and ESLint on changed files.

Closes #1240
Closes #1238
Closes #1230
Closes #1229

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