feat: add C++ language support and hook tests (#539)

- agents: cpp-build-resolver, cpp-reviewer
- commands: cpp-build, cpp-review, cpp-test
- rules: cpp/ (coding-style, hooks, patterns, security, testing)
- tests: 9 new hook test files with comprehensive coverage

Cherry-picked from PR #436.

rules/cpp/patterns.md

@@ -0,0 +1,51 @@
+---
+paths:
+  - "**/*.cpp"
+  - "**/*.hpp"
+  - "**/*.cc"
+  - "**/*.hh"
+  - "**/*.cxx"
+  - "**/*.h"
+  - "**/CMakeLists.txt"
+---
+# C++ Patterns
+
+> This file extends [common/patterns.md](../common/patterns.md) with C++ specific content.
+
+## RAII (Resource Acquisition Is Initialization)
+
+Tie resource lifetime to object lifetime:
+
+```cpp
+class FileHandle {
+public:
+    explicit FileHandle(const std::string& path) : file_(std::fopen(path.c_str(), "r")) {}
+    ~FileHandle() { if (file_) std::fclose(file_); }
+    FileHandle(const FileHandle&) = delete;
+    FileHandle& operator=(const FileHandle&) = delete;
+private:
+    std::FILE* file_;
+};
+```
+
+## Rule of Five/Zero
+
+- **Rule of Zero**: Prefer classes that need no custom destructor, copy/move constructors, or assignments
+- **Rule of Five**: If you define any of destructor/copy-ctor/copy-assign/move-ctor/move-assign, define all five
+
+## Value Semantics
+
+- Pass small/trivial types by value
+- Pass large types by `const&`
+- Return by value (rely on RVO/NRVO)
+- Use move semantics for sink parameters
+
+## Error Handling
+
+- Use exceptions for exceptional conditions
+- Use `std::optional` for values that may not exist
+- Use `std::expected` (C++23) or result types for expected failures
+
+## Reference
+
+See skill: `cpp-coding-standards` for comprehensive C++ patterns and anti-patterns.