[Backend] Establish standalone build infrastructure

Add the thin monorepo CMake entry point and an independently configurable backend project. Enforce the Clang/C++23 toolchain, expose Make/Ninja-neutral tests and developer checks, export an installable RCCBackend package, and introduce the first Support error abstraction.

1 files changed, 49 insertions, 0 deletions

diff --git a/backend/.clang-tidy b/backend/.clang-tidy
new file mode 100644
index 0000000..a0e18ce
--- /dev/null
+++ b/backend/.clang-tidy
@@ -0,0 +1,49 @@
+HeaderFilterRegex: '(^|/)(include|lib|tools|utils|unittests)/'
+WarningsAsErrors: ''
+FormatStyle: file
+Checks: >
+  -*,
+  clang-diagnostic-*,
+  bugprone-*,
+  -bugprone-easily-swappable-parameters,
+  performance-*,
+  portability-*,
+  llvm-header-guard,
+  llvm-namespace-comment,
+  llvm-qualified-auto,
+  misc-definitions-in-headers,
+  misc-misplaced-const,
+  misc-new-delete-overloads,
+  misc-non-copyable-objects,
+  modernize-use-default-member-init,
+  modernize-use-equals-default,
+  modernize-use-equals-delete,
+  modernize-use-nullptr,
+  modernize-use-override,
+  readability-container-size-empty,
+  readability-identifier-naming,
+  readability-redundant-*,
+  readability-simplify-boolean-expr
+
+CheckOptions:
+  - { key: readability-identifier-naming.NamespaceCase,             value: lower_case }
+  - { key: readability-identifier-naming.ClassCase,                 value: CamelCase  }
+  - { key: readability-identifier-naming.StructCase,                value: CamelCase  }
+  - { key: readability-identifier-naming.UnionCase,                 value: CamelCase  }
+  - { key: readability-identifier-naming.EnumCase,                  value: CamelCase  }
+  - { key: readability-identifier-naming.TypeAliasCase,             value: CamelCase  }
+  - { key: readability-identifier-naming.TypedefCase,               value: CamelCase  }
+  - { key: readability-identifier-naming.TypeTemplateParameterCase, value: CamelCase  }
+  - { key: readability-identifier-naming.FunctionCase,              value: camelBack  }
+  - { key: readability-identifier-naming.MethodCase,                value: camelBack  }
+  - { key: readability-identifier-naming.VariableCase,              value: CamelCase  }
+  - { key: readability-identifier-naming.ParameterCase,             value: CamelCase  }
+  - { key: readability-identifier-naming.MemberCase,                value: CamelCase  }
+  - { key: readability-identifier-naming.GlobalConstantCase,        value: CamelCase  }
+  - { key: readability-identifier-naming.ConstexprVariableCase,     value: CamelCase  }
+  - { key: readability-identifier-naming.ClassConstantCase,         value: CamelCase  }
+  - { key: readability-identifier-naming.EnumConstantCase,          value: CamelCase  }
+  - { key: readability-identifier-naming.MacroDefinitionCase,       value: UPPER_CASE }
+  - { key: readability-identifier-naming.IgnoreMainLikeFunctions,   value: 1          }
+  - { key: readability-redundant-member-init.IgnoreBaseInCopyConstructors, value: 1    }
+  - { key: modernize-use-default-member-init.UseAssignment,         value: 1          }