refactor(lint): rewrite structural linters from Ruby to PHP

Fold scripts/lint and scripts/linters/*.rb into a standalone Composer
project under scripts/linters/, matching the scripts/plugin-class-classifier/
convention. Uses no external packages, only PHP + Composer autoloading.

Verified byte-for-byte identical output against the original Ruby
implementation, both on the current repo (all linters pass) and on a
synthetic fixture exercising every violation type.

Entry point moves from `scripts/lint` to `scripts/linters/lint`.

1 files changed, 19 insertions, 0 deletions

diff --git a/scripts/linters/src/Linter.php b/scripts/linters/src/Linter.php
new file mode 100644
index 00000000..3fb6038f
--- /dev/null
+++ b/scripts/linters/src/Linter.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Shirabe\Lint;
+
+interface Linter
+{
+    public function name(): string;
+
+    /**
+     * @param list<string> $excludes root-relative paths to skip
+     * @return list<string> formatted violation lines; empty when the linter passes
+     */
+    public function check(string $rootDir, array $excludes): array;
+
+    /** Printed once, above the violation list, when violations are found. */
+    public function failureIntro(): string;
+}