Add slippage impact override protection

[Gojv-byte]

Summary

• Persist the slippage tolerance preference (1% default).
• Show a live price-impact warning when impact exceeds tolerance; require acknowledgement before submitting.
• Add coverage for preference persistence and buy/sell trade flows.

closes #995

Testing

• pnpm lint
• pnpm build
• Focused trade and preference tests (41 passed)
• Full pnpm test (130 tests failed across 50 files)

Checklist

• Linked issue or backlog item
• Scope is limited to the stated change
• Updated docs if behavior or setup changed
• Added screenshots for UI changes when relevant

[drips-wave]

@Gojv-byte Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

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