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.

commands/cpp-review.md

@@ -0,0 +1,132 @@
+---
+description: Comprehensive C++ code review for memory safety, modern C++ idioms, concurrency, and security. Invokes the cpp-reviewer agent.
+---
+
+# C++ Code Review
+
+This command invokes the **cpp-reviewer** agent for comprehensive C++-specific code review.
+
+## What This Command Does
+
+1. **Identify C++ Changes**: Find modified `.cpp`, `.hpp`, `.cc`, `.h` files via `git diff`
+2. **Run Static Analysis**: Execute `clang-tidy` and `cppcheck`
+3. **Memory Safety Scan**: Check for raw new/delete, buffer overflows, use-after-free
+4. **Concurrency Review**: Analyze thread safety, mutex usage, data races
+5. **Modern C++ Check**: Verify code follows C++17/20 conventions and best practices
+6. **Generate Report**: Categorize issues by severity
+
+## When to Use
+
+Use `/cpp-review` when:
+- After writing or modifying C++ code
+- Before committing C++ changes
+- Reviewing pull requests with C++ code
+- Onboarding to a new C++ codebase
+- Checking for memory safety issues
+
+## Review Categories
+
+### CRITICAL (Must Fix)
+- Raw `new`/`delete` without RAII
+- Buffer overflows and use-after-free
+- Data races without synchronization
+- Command injection via `system()`
+- Uninitialized variable reads
+- Null pointer dereferences
+
+### HIGH (Should Fix)
+- Rule of Five violations
+- Missing `std::lock_guard` / `std::scoped_lock`
+- Detached threads without proper lifetime management
+- C-style casts instead of `static_cast`/`dynamic_cast`
+- Missing `const` correctness
+
+### MEDIUM (Consider)
+- Unnecessary copies (pass by value instead of `const&`)
+- Missing `reserve()` on known-size containers
+- `using namespace std;` in headers
+- Missing `[[nodiscard]]` on important return values
+- Overly complex template metaprogramming
+
+## Automated Checks Run
+
+```bash
+# Static analysis
+clang-tidy --checks='*,-llvmlibc-*' src/*.cpp -- -std=c++17
+
+# Additional analysis
+cppcheck --enable=all --suppress=missingIncludeSystem src/
+
+# Build with warnings
+cmake --build build -- -Wall -Wextra -Wpedantic
+```
+
+## Example Usage
+
+```text
+User: /cpp-review
+
+Agent:
+# C++ Code Review Report
+
+## Files Reviewed
+- src/handler/user.cpp (modified)
+- src/service/auth.cpp (modified)
+
+## Static Analysis Results
+✓ clang-tidy: 2 warnings
+✓ cppcheck: No issues
+
+## Issues Found
+
+[CRITICAL] Memory Leak
+File: src/service/auth.cpp:45
+Issue: Raw `new` without matching `delete`
+```cpp
+auto* session = new Session(userId);  // Memory leak!
+cache[userId] = session;
+```
+Fix: Use `std::unique_ptr`
+```cpp
+auto session = std::make_unique<Session>(userId);
+cache[userId] = std::move(session);
+```
+
+[HIGH] Missing const Reference
+File: src/handler/user.cpp:28
+Issue: Large object passed by value
+```cpp
+void processUser(User user) {  // Unnecessary copy
+```
+Fix: Pass by const reference
+```cpp
+void processUser(const User& user) {
+```
+
+## Summary
+- CRITICAL: 1
+- HIGH: 1
+- MEDIUM: 0
+
+Recommendation: ❌ Block merge until CRITICAL issue is fixed
+```
+
+## Approval Criteria
+
+| Status | Condition |
+|--------|-----------|
+| ✅ Approve | No CRITICAL or HIGH issues |
+| ⚠️ Warning | Only MEDIUM issues (merge with caution) |
+| ❌ Block | CRITICAL or HIGH issues found |
+
+## Integration with Other Commands
+
+- Use `/cpp-test` first to ensure tests pass
+- Use `/cpp-build` if build errors occur
+- Use `/cpp-review` before committing
+- Use `/code-review` for non-C++ specific concerns
+
+## Related
+
+- Agent: `agents/cpp-reviewer.md`
+- Skills: `skills/cpp-coding-standards/`, `skills/cpp-testing/`