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

crates/formatrix-core/src/lib.rs

@@ -7,6 +7,7 @@
 //! - Implementations for 7 formats: TXT, MD, ADOC, DJOT, ORG, RST, TYP
 //! - C FFI exports for the Ada TUI (FD-M10)
 
+#![forbid(unsafe_code)]
 pub mod ast;
 pub mod file_ops;
 pub mod formats;

crates/formatrix-gui/src/lib.rs

@@ -1,6 +1,7 @@
 // SPDX-License-Identifier: PMPL-1.0-or-later
 //! Formatrix GUI - Tauri 2.0 desktop and mobile application
 
+#![forbid(unsafe_code)]
 pub mod commands;
 
 pub use commands::*;

crates/formatrix-pipeline/src/lib.rs

@@ -6,6 +6,7 @@
 //! - Steps: Ordered list of transforms
 //! - Output: Target format and filename pattern
 
+#![forbid(unsafe_code)]
 use serde::{Deserialize, Serialize};
 use thiserror::Error;