chore: remove unnecessary blank line in README for migration documentation

Author: Marvin Zhang

specs/018-golang-to-rust-migration/README.md

@@ -19,7 +19,6 @@ transitions:
 completed_at: '2025-12-18T01:17:59.487Z'
 completed: '2025-12-18'
 ---
-
 # Migrate Devlog from Go to Rust
 
 > **Status**: ✅ Complete · **Priority**: High · **Created**: 2025-12-18 · **Tags**: migration, rust, backend, architecture, rewrite