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-build.md

@@ -0,0 +1,173 @@
+---
+description: Fix C++ build errors, CMake issues, and linker problems incrementally. Invokes the cpp-build-resolver agent for minimal, surgical fixes.
+---
+
+# C++ Build and Fix
+
+This command invokes the **cpp-build-resolver** agent to incrementally fix C++ build errors with minimal changes.
+
+## What This Command Does
+
+1. **Run Diagnostics**: Execute `cmake --build`, `clang-tidy`, `cppcheck`
+2. **Parse Errors**: Group by file and sort by severity
+3. **Fix Incrementally**: One error at a time
+4. **Verify Each Fix**: Re-run build after each change
+5. **Report Summary**: Show what was fixed and what remains
+
+## When to Use
+
+Use `/cpp-build` when:
+- `cmake --build build` fails with errors
+- Linker errors (undefined references, multiple definitions)
+- Template instantiation failures
+- Include/dependency issues
+- After pulling changes that break the build
+
+## Diagnostic Commands Run
+
+```bash
+# CMake configure
+cmake -B build -S .
+
+# Build
+cmake --build build 2>&1 | head -100
+
+# Static analysis (if available)
+clang-tidy src/*.cpp -- -std=c++17
+cppcheck --enable=all src/
+```
+
+## Example Session
+
+```text
+User: /cpp-build
+
+Agent:
+# C++ Build Resolution
+
+## Initial Diagnostics
+
+```bash
+$ cmake --build build
+src/service/user.cpp:25:15: error: use of undeclared identifier 'UserRepository'
+src/handler/api.cpp:42:9: error: no matching function for call to 'process'
+src/handler/api.cpp:58:1: error: non-void function does not return a value
+```
+
+Errors found: 3
+
+## Fix 1: Undeclared Identifier
+
+File: src/service/user.cpp:25
+Error: use of undeclared identifier 'UserRepository'
+Cause: Missing include
+
+```cpp
+// Added include
+#include "repository/user_repository.hpp"
+```
+
+```bash
+$ cmake --build build
+# 2 errors remaining
+```
+
+## Fix 2: No Matching Function
+
+File: src/handler/api.cpp:42
+Error: no matching function for call to 'process'
+
+```cpp
+// Changed
+process(params.get("count"));
+// To
+process(std::stoi(params.get("count")));
+```
+
+```bash
+$ cmake --build build
+# 1 error remaining
+```
+
+## Fix 3: Missing Return
+
+File: src/handler/api.cpp:58
+Error: non-void function does not return a value
+
+```cpp
+std::optional<User> getUser(const std::string& id) {
+    if (id.empty()) {
+        return std::nullopt;
+    }
+    auto user = findUser(id);
+    // Added missing return
+    return user;
+}
+```
+
+```bash
+$ cmake --build build
+# Build successful!
+```
+
+## Final Verification
+
+```bash
+$ ctest --test-dir build --output-on-failure
+Test project build
+    1/5 Test #1: unit_tests ........   Passed    0.02 sec
+    2/5 Test #2: integration_tests    Passed    0.15 sec
+All tests passed.
+```
+
+## Summary
+
+| Metric | Count |
+|--------|-------|
+| Build errors fixed | 3 |
+| Linker errors fixed | 0 |
+| Files modified | 2 |
+| Remaining issues | 0 |
+
+Build Status: ✅ SUCCESS
+```
+
+## Common Errors Fixed
+
+| Error | Typical Fix |
+|-------|-------------|
+| `undeclared identifier` | Add `#include` or fix typo |
+| `no matching function` | Fix argument types or add overload |
+| `undefined reference` | Link library or add implementation |
+| `multiple definition` | Use `inline` or move to .cpp |
+| `incomplete type` | Replace forward decl with `#include` |
+| `no member named X` | Fix member name or include |
+| `cannot convert X to Y` | Add appropriate cast |
+| `CMake Error` | Fix CMakeLists.txt configuration |
+
+## Fix Strategy
+
+1. **Compilation errors first** - Code must compile
+2. **Linker errors second** - Resolve undefined references
+3. **Warnings third** - Fix with `-Wall -Wextra`
+4. **One fix at a time** - Verify each change
+5. **Minimal changes** - Don't refactor, just fix
+
+## Stop Conditions
+
+The agent will stop and report if:
+- Same error persists after 3 attempts
+- Fix introduces more errors
+- Requires architectural changes
+- Missing external dependencies
+
+## Related Commands
+
+- `/cpp-test` - Run tests after build succeeds
+- `/cpp-review` - Review code quality
+- `/verify` - Full verification loop
+
+## Related
+
+- Agent: `agents/cpp-build-resolver.md`
+- Skill: `skills/cpp-coding-standards/`