chore(nix): remove statix and deadnix from fixer

Drop the statix and deadnix packages from the fix app now that the repository has a local Nix style linter path. Remove the obsolete statix configuration, document the evaluated rule sets and architectures, and keep vendored third-party files out of treefmt.

AGENTS.md

@@ -98,9 +98,14 @@
 - Rust tests in this monorepo live in separate `*_test.rs` files, not inline `#[cfg(test)]` modules.
 - Ariadne Rust tests are declared in Bazel `BUILD` files; do not add `[[test]]` entries to
   `src/ariadne/Cargo.toml` unless explicitly requested.
+- Rust package validation in this monorepo uses Bazel `rust_test` targets.
+  Do not claim or require `cargo test` as the standard Rust validation path unless explicitly requested.
 - In this monorepo, "dotfiles" refers to the dotfiles/NixOS configuration under `src/dotfiles/` and `configs/nixos/`.
 - The flake does not currently define `formatter.x86_64-linux`.
   Do not use `nix fmt` as a validation command until a formatter is added.
+- Keep `third_party/**` excluded from treefmt.
+  Vendored code can contain syntax fixtures, generated files, or upstream formatting that local
+  formatters must not rewrite.
 - Ariadne extraction must preserve the game-root season prefix for archived source.
   Different game installs can contain compiled scripts with the same internal path.
 - Clew owns Ren'Py extraction, preparation, and compiled-script AST export. Ariadne owns analysis over Clew-produced data.
@@ -114,3 +119,5 @@
   Do not use `git subtree add` or `git subtree pull` for Pi PR branches.
   Gitea rebases the synthetic upstream root commit without the `third_party/pi` prefix.
   Preserve `git-subtree-dir` and `git-subtree-split` trailers on Pi vendor commits.
+- `rules_rust` `crates_vendor` can vendor direct crate specs through the `packages` attribute.
+  Do not create a placeholder Rust package only to anchor a future vendored dependency.