Define missing governance types used by module code

**Area:** Contracts
**Files:** `contracts/predict-iq/src/types.rs`, `contracts/predict-iq/src/modules/governance.rs`

**Problem:** Governance references `UpgradeStats` and `PendingGuardianRemoval` types that are not present in `types.rs`.

**Acceptance Criteria:**
- Missing structs are defined with contracttype derives.
- Serialization compatibility is tested.
- Contract builds and tests pass.