Fix documentation inconsistencies and bump document versions

Rust/DESIGN_DOCUMENT_LIB.md

@@ -1,6 +1,6 @@
 # Rust Library Development Guidelines
 
-**Document Version:** v1
+**Document Version:** v2
 
 > **Note on Versioning:**
 > - This document version is independent — reused across projects
@@ -28,6 +28,7 @@ The root directory contains only the core documents: `README.md`, `AGENTS.md`, `
 
 - **Rust edition:** 2024 (requires Rust 1.85 or newer)
 - Declare the minimum toolchain in `Cargo.toml` (`rust-version = "1.85"`) so consumers get a clear error instead of a compile failure
+- **100-character lines** (rustfmt default `max_width`)
 - Format with **rustfmt** — run `cargo fmt` before every commit
 - Lint with **clippy** — run `cargo clippy -- -D warnings` before every commit
 - **snake_case** functions/variables/modules, **PascalCase** types/traits, **SCREAMING_SNAKE_CASE** constants
@@ -169,8 +170,6 @@ mod tests {
 }
 ```
 
-`Cargo.lock` is **not committed** for libraries — add it to `.gitignore`. Consumers pin their own dependency graph.
-
 ---
 
 ## 9. Documentation