feat: implement global pause


**Description**
Global pause switch.

**Problem Statement**
No way to stop protocol.

**Technical Requirements**
- [ ] Pause modifier.

**Implementation Guide**
- **Suggested Approach:** Toggle pause state.
- **Affected Areas:** src/

**Acceptance Criteria**
- [ ] Admin can pause.

**Security & Audit Considerations**
- [ ] Multi-sig restricted.

**Definition of Done**
- [ ] Verified.