chore: add agentic tooling, cleanup

.crosslink/rules/cpp.md

@@ -0,0 +1,39 @@
+### C++ Best Practices
+
+#### Modern C++ (C++17+)
+- Use smart pointers (`unique_ptr`, `shared_ptr`) over raw pointers
+- Use RAII for resource management
+- Prefer `std::string` and `std::vector` over C arrays
+- Use `auto` for complex types, explicit types for clarity
+
+```cpp
+// GOOD: Modern C++ with smart pointers
+auto config = std::make_unique<Config>();
+auto users = std::vector<User>{};
+
+// BAD: Manual memory management
+Config* config = new Config();
+// ... forgot to delete
+```
+
+#### Error Handling
+- Use exceptions for exceptional cases
+- Use `std::optional` for values that may not exist
+- Use `std::expected` (C++23) or result types for expected failures
+
+```cpp
+// GOOD: Optional for missing values
+std::optional<User> findUser(const std::string& id) {
+    auto it = users.find(id);
+    if (it == users.end()) {
+        return std::nullopt;
+    }
+    return it->second;
+}
+```
+
+#### Security
+- Validate all input boundaries
+- Use `std::string_view` for non-owning string references
+- Avoid C-style casts; use `static_cast`, `dynamic_cast`
+- Never use `sprintf`; use `std::format` or streams