fix: guard risk-pool withdrawals when capital is drained

[iamcracked-dev]

Closes #668
Closes #648
Closes #649
Closes #650

Summary

This pull request makes the fully utilized and drained risk-pool state explicit during LP redemption. When all deposited capital is locked, there is no valid share price or withdrawable liquidity to calculate, so the contract now returns a dedicated typed error instead of treating the condition as a generic collateral failure.

Issue #668: Guard drained-pool withdrawals

• Added the PoolDrained contract error for the no-unlocked-liquidity state.
• Applied the guard to the normal withdrawal path.
• Applied the same guard to the admin-approved emergency withdrawal path.
• Preserved the existing arithmetic and balance checks for partially utilized pools.
• Prevented withdrawal math from proceeding when total locked capital consumes the entire deposited balance.

Assigned issue references

The description includes both assigned Parashield Contracts issues: #668 and #648. The implementation is focused on the drained-pool behavior described by #668; the existing source already contains the disputed-claim status guard associated with #648.

Verification

Not run, per request. No installation, build, test, or CI check was performed.

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