chore: add #![forbid(unsafe_code)] to safe Rust crates

Adds the forbid(unsafe_code) crate-level attribute to all Rust crates
that do not use unsafe code, hardening the safety guarantee at compile
time.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hyperpolymath

echidnabot/src/lib.rs

@@ -11,6 +11,7 @@
 //!
 //! See `docs/ARCHITECTURE.adoc` for the full design document.
 
+#![forbid(unsafe_code)]
 pub mod api;
 pub mod adapters;
 pub mod config;