chore: update Epic 2 status to In Progress (2.4, 2.5 done)

Author: 0xfave

docs/epics/epic-2-smart-contract.md

@@ -1,6 +1,6 @@
 # Epic 2: Smart Contract Instructions (L4)
 
-**Status:** Not Started
+**Status:** In Progress
 **Priority:** P0 — Core protocol logic
 **Depends on:** Epic 1 complete (state.rs, instruction.rs, error.rs, testing infra)