chore: remove "nix build" instruction for development

docs/design/workflows-public-dogfood-split.md

@@ -87,7 +87,7 @@ These remain in this repository under `.yoi/workflow/` as overrides or dogfood-o
   - `.yoi/memory`, local/runtime/log/lock/secret-like paths excluded;
   - branch/worktree cleanup policy.
 - A dogfood extension for multi-agent/merge-completion, if the generic builtin `multi-agent-workflow` is cleaned:
-  - concrete `cargo fmt`, `cargo test`, `target/debug/yoi ticket doctor`, `nix build .#yoi` validation policy;
+  - concrete `cargo fmt`, `cargo test`, `target/debug/yoi ticket doctor`, validation policy;
   - merge authority boundaries for this repository;
   - docs/report conventions.
 

docs/development/work-items.md

@@ -427,7 +427,6 @@ Implementation Tickets usually also need focused tests and broader checks, for e
 cargo fmt --check
 cargo check --workspace --all-targets
 cargo test -p <crate> <filter>
-nix build .#yoi --no-link
 ```
 
 Record validation commands and results in the implementation report or resolution.