📝 docs(playbook): add contributing and multi-language standards

Introduce C++ and Python docs/templates and split .agents rulesets by language (tsl/cpp/python).

Move commit message guidance to CONTRIBUTING.md (full spec remains in docs/common/commit_message.md).

.gitattributes

@@ -19,6 +19,29 @@
 *.xml   text eol=lf
 *.csv   text eol=lf
 *.sh    text eol=lf
+*.py    text eol=lf
+*.pyi   text eol=lf
+*.pyx   text eol=lf
+*.pxd   text eol=lf
+*.pxi   text eol=lf
+*.c     text eol=lf
+*.h     text eol=lf
+*.cc    text eol=lf
+*.cpp   text eol=lf
+*.cxx   text eol=lf
+*.hh    text eol=lf
+*.hpp   text eol=lf
+*.hxx   text eol=lf
+*.inl   text eol=lf
+*.ipp   text eol=lf
+*.ixx   text eol=lf
+*.cppm  text eol=lf
+*.mpp   text eol=lf
+*.cmake text eol=lf
+CMakeLists.txt text eol=lf
+CMakePresets.json text eol=lf
+*.clangd text eol=lf
+.clangd text eol=lf
 
 # Binary files (no line-ending conversion).
 *.png   binary