refactor: consolidate #![allow(clippy::cast_*)] to crate roots

Add the cast-allow block to zesdex-entities/src/lib.rs and
zesdex-utils/src/lib.rs (which lacked it), then remove from
65 sub-files across all 8 crates. Build and all 223 tests
continue to pass.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/zesdex-backend/src/app/runtime/actions/mod.rs

@@ -16,8 +16,6 @@
 //! running turns on plain OS threads (rather than blocking the main loop)
 //! keeps the TUI responsive while the LLM streams.
 
-#![allow(clippy::cast_possible_truncation, clippy::cast_sign_loss, clippy::cast_precision_loss, clippy::cast_possible_wrap)]
-
 mod handlers;
 mod io;
 mod memory;