feat: initialise core/lint module

Go module, .core/build.yaml, CLAUDE.md, directory structure.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.core/build.yaml

@@ -0,0 +1,25 @@
+version: 1
+
+project:
+  name: core-lint
+  description: Pattern catalog and regex code checker
+  main: ./cmd/core-lint
+  binary: core-lint
+
+build:
+  cgo: false
+  flags:
+    - -trimpath
+  ldflags:
+    - -s
+    - -w
+
+targets:
+  - os: linux
+    arch: amd64
+  - os: linux
+    arch: arm64
+  - os: darwin
+    arch: arm64
+  - os: windows
+    arch: amd64

CLAUDE.md

@@ -0,0 +1,30 @@
+# CLAUDE.md
+
+## Project Overview
+
+`core/lint` is a standalone pattern catalog and regex-based code checker. It loads YAML rule definitions and matches them against source files. Zero framework dependencies.
+
+## Build & Development
+
+```bash
+core go test
+core go qa
+core build          # produces ./bin/core-lint
+```
+
+## Architecture
+
+- `catalog/` — YAML rule files (embedded at compile time)
+- `pkg/lint/` — Library: Rule, Catalog, Matcher, Scanner, Report types
+- `cmd/core-lint/` — CLI binary using `cli.Main()`
+
+## Rule Schema
+
+Each YAML file contains an array of rules with: id, title, severity, languages, tags, pattern (regex), exclude_pattern, fix, example_bad, example_good, detection type.
+
+## Coding Standards
+
+- UK English
+- All functions have typed params/returns
+- Tests use testify
+- License: EUPL-1.2

go.mod

@@ -0,0 +1,3 @@
+module forge.lthn.ai/core/lint
+
+go 1.26.0