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/coding-style.md

@@ -0,0 +1,44 @@
+---
+paths:
+  - "**/*.cpp"
+  - "**/*.hpp"
+  - "**/*.cc"
+  - "**/*.hh"
+  - "**/*.cxx"
+  - "**/*.h"
+  - "**/CMakeLists.txt"
+---
+# C++ Coding Style
+
+> This file extends [common/coding-style.md](../common/coding-style.md) with C++ specific content.
+
+## Modern C++ (C++17/20/23)
+
+- Prefer **modern C++ features** over C-style constructs
+- Use `auto` when the type is obvious from context
+- Use `constexpr` for compile-time constants
+- Use structured bindings: `auto [key, value] = map_entry;`
+
+## Resource Management
+
+- **RAII everywhere** — no manual `new`/`delete`
+- Use `std::unique_ptr` for exclusive ownership
+- Use `std::shared_ptr` only when shared ownership is truly needed
+- Use `std::make_unique` / `std::make_shared` over raw `new`
+
+## Naming Conventions
+
+- Types/Classes: `PascalCase`
+- Functions/Methods: `snake_case` or `camelCase` (follow project convention)
+- Constants: `kPascalCase` or `UPPER_SNAKE_CASE`
+- Namespaces: `lowercase`
+- Member variables: `snake_case_` (trailing underscore) or `m_` prefix
+
+## Formatting
+
+- Use **clang-format** — no style debates
+- Run `clang-format -i <file>` before committing
+
+## Reference
+
+See skill: `cpp-coding-standards` for comprehensive C++ coding standards and guidelines.