docs: comprehensive README with v0.6.0 gene mutation system, contributing & security policy

- Add v0.6.0 synthetic gene mutation system section (from REFRACTORING-v0.6.0.md)
- Add contributing guidelines, security policy, language breakdown
- Add badge bar, mutation threat row, topics tags
- No existing content removed

shared/src/vm_extensions.rs

@@ -12,7 +12,7 @@ use serde::{Deserialize, Serialize};
 // NOTE: stack effect notation:
 //   +1  => pushes one u32
 //   -1  => pops one u32
-//   0   => net-zero (or no stack interaction)
+//    0  => net-zero (or no stack interaction)
 //
 // Security/performance notes:
 // - All index operands are normalized with modulo to avoid panics.