Vendor crabrl-fork source and remove submodule linkage

- Replace `rust/crabrl-fork` gitlink with tracked source files
- Add workspace notes documenting why the fork is vendored
- Update ignore rules for vendored fork build artifacts

rust/crabrl-fork/.gitattributes

@@ -0,0 +1,55 @@
+# Auto detect text files and perform LF normalization
+* text=auto
+
+# Rust files
+*.rs text eol=lf
+*.toml text eol=lf
+Cargo.lock text eol=lf
+
+# Python files
+*.py text eol=lf
+*.pyx text eol=lf
+*.pxd text eol=lf
+
+# Documentation
+*.md text eol=lf
+*.txt text eol=lf
+LICENSE text eol=lf
+
+# Config files
+*.json text eol=lf
+*.yaml text eol=lf
+*.yml text eol=lf
+*.xml text eol=lf
+*.xsd text eol=lf
+*.xbrl text eol=lf
+
+# Shell scripts
+*.sh text eol=lf
+*.bash text eol=lf
+
+# Git files
+.gitignore text eol=lf
+.gitattributes text eol=lf
+
+# Binary files
+*.png binary
+*.jpg binary
+*.jpeg binary
+*.gif binary
+*.ico binary
+*.pdf binary
+*.zip binary
+*.gz binary
+*.tar binary
+*.7z binary
+*.exe binary
+*.dll binary
+*.so binary
+*.dylib binary
+
+# Linguist overrides - ensure Rust is recognized as primary language
+*.rs linguist-language=Rust
+benchmarks/*.py linguist-documentation
+scripts/*.py linguist-documentation
+examples/* linguist-documentation