Initial import: the house-style lint rules as a crafter-build module

Moved out of Crafter.Build's lint-rules.h so a project.cpp pulls them in
with `#pragma crafter dependency` + `import Crafter.LintRules;` instead of
copying a header. The rule bodies are unchanged; format-concat now sits
with the other transforms (it rewrites, it was registered as a report),
and the helpers are module-internal. tests/HouseRules moved along with
the rules and links crafter-build from git, or the sibling checkout with
--local.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

README.md

@@ -0,0 +1,60 @@
+# Crafter.LintRules
+
+The Catcrafts house-style lint rules for [crafter-build](https://forgejo.catcrafts.net/Catcrafts/Crafter.Build), packaged as one C++ module. Naming conventions, K&R braces, `enum class`, `std::println` over iostream, fixed-width integer types, `std::format` over concatenation, line wrapping, whitespace hygiene and a few AST-backed checks (`const` locals, `constexpr` constants, no `char*`). Most rules are transforms, so `crafter-build format` applies them.
+
+## Use
+
+In a `project.cpp`:
+
+```cpp
+import std;
+import Crafter.Build;
+#pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.LintRules.git"
+import Crafter.LintRules;
+using namespace Crafter;
+
+extern "C" Configuration CrafterBuildProject(std::span<const std::string_view> args) {
+    Configuration cfg;
+    // ...
+    LintRules::AddRules(cfg);
+    return cfg;
+}
+```
+
+Then `crafter-build lint` reports, `crafter-build format` rewrites, and `crafter-build format --check` gates CI. Pin a revision for reproducible builds:
+
+```cpp
+#pragma crafter dependency "https://forgejo.catcrafts.net/Catcrafts/Crafter.LintRules.git" commit "<sha>"
+```
+
+Suppress a finding with `// lint-disable-next-line <rule>` or a whole file with `// lint-disable-file <rule>`.
+
+## Rules
+
+| Rule | Kind | What it wants |
+| --- | --- | --- |
+| `spdx-header` | report | `// SPDX-License-Identifier:` on line 1, `// SPDX-FileCopyrightText:` on line 2, blank line 3 |
+| `no-tabs` | report | spaces |
+| `naming` | report, AST | PascalCase types, functions, statics and constants; camelCase variables |
+| `enum-class` | report | `enum class`, never a plain `enum` |
+| `no-iostream-print` | report | `std::println` instead of `std::cout`/`std::cerr` streaming |
+| `no-char-pointer` | report, AST | `std::string` / `std::string_view` over `char*` outside C interop |
+| `const-local` | report, AST | `const` on a scalar local that is never written |
+| `constexpr-constant` | report, AST | `constexpr` on a constant with a constant initialiser |
+| `format-concat` | transform | `std::format` instead of `+` with string literals |
+| `fixed-width-types` | transform, AST | `std::int32_t` and friends instead of `int`, `long`, … |
+| `single-declaration` | transform, AST | one declaration per statement |
+| `brace-style` | transform | K&R braces |
+| `if-single-line` | transform | `if (x) return;` on one line when it fits |
+| `wrap-join` | transform | join wrapped statements that fit on one line |
+| `paren-spacing` | transform | `if (` and `for (`, no space before a call's `(` |
+| `trim-trailing-ws` | transform | no trailing whitespace |
+| `final-newline` | transform | files end with a newline |
+
+## Tests
+
+`tests/HouseRules` exercises every rule against small inputs. It links crafter-build to run the linter in-process, so it fetches and builds it from git; with a sibling checkout at `../Crafter.Build` use `crafter-build test --local`.
+
+## Building for other targets
+
+The module imports `Crafter.Build`, which only exists for the host. That is all a rule ever needs: rules run inside the crafter-build process that loads your `project.cpp`.