feat: implement protocol-wide emergency pause via parameters-contract

[EmeditWeb]

Problem

There is no emergency pause mechanism anywhere in the contract suite. The product vision specifies a kill-switch that can halt all protocol operations in case of an emergency (e.g., vulnerability discovered, oracle malfunction).

Contract impact: If a critical vulnerability is discovered, there is no way to pause the protocol. All contract operations would continue until a WASM upgrade is deployed and activated — a process that takes time during which funds can be lost.

Before Starting

Read: context/architecture-context.md

Root Cause

The pause mechanism was deferred in the contract design.

What To Build

1. Add paused: bool to parameters contract storage
2. Add set_paused(env, admin, paused: bool) — admin/multisig only
3. All other contracts read pause status from parameters contract
4. When paused, all mutating functions return a Paused error
5. Read-only functions (get_score, get_loan, etc.) still work when paused

Files To Touch

• contracts/parameters-contract/src/lib.rs — add pause/unpause
• contracts/parameters-contract/src/storage.rs — add paused key
• contracts/creditline-contract/src/lib.rs — check pause before mutations
• contracts/liquidity-pool-contract/src/lib.rs — check pause before mutations
• contracts/reputation-contract/src/lib.rs — check pause before mutations

Acceptance Criteria

• Pause flag stored in parameters contract
• Admin can pause/unpause
• All mutating functions blocked when paused
• Read functions work when paused
• All existing tests pass

Mandatory Checks

• context/ files read
• cargo build passes
• cargo test passes
• PR references this issue