Feature/emergency withdraw

[Abidoyesimze]

closes #119

Summary

Adds a guaranteed emergency withdrawal path to let users exit directly from idle vault reserves if the main app/strategies are compromised, plus a minimal independently hostable UI page.
Motivation
If the frontend fails or a strategy appears unsafe, users need a simple, reliable escape hatch that avoids strategy interactions and queues.

What’s Included

Contract: yield_vault
emergency_withdraw(to, shares): burns shares and pays from idle reserves only.
set_emergency_penalty(admin, bps): optional haircut during emergency exits.
Events: emg_wd, emg_pen.
Internal accounting updates to maintain invariants.

Tests

Emulates partial allocation to strategy; withdraws only the idle portion.
Validates penalty application.
Minimal UI: emergency-ui Next.js app
/emergency page with clear warning and simple form (contract id, address, shares).
Designed for independent hosting (Vercel/IPFS).

Security

Skips external strategy/oracle calls; uses only contract’s token balance.
Burns shares and clamps to idle reserves, preventing over-withdraws.
Optional penalty (bps) set by admin.
Note: If/when per-user debt is added, gate emergency_withdraw behind a “no-active-debt(user)” check.

How to Test

Contracts:
From contracts/: cargo test -p yield_vault emergency::tests::
UI (optional):
cd emergency-ui && npm install && npm run build && npm start

Acceptance Criteria Mapping

Implement an emergency_withdraw that bypasses strategies: done.
Pulls from idle reserves only: enforced via contract balance.
Minimal independent /emergency page with warnings: added.
Warning about penalties/slippage: present in UI.
Security: no strategy calls; penalty optional; future hook for debt checks.

Checklist

[x] Contract functions and events
[x] Tests for idle-only and penalty cases
[x] Minimal emergency UI with warning
[x] Docs/comments on usage and security caveats

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[edehvictor]

@Abidoyesimze fix CI error