fix(scripts): exempt .env template files from diff-coverage gate

.env.example and siblings are config/template files with no executable
code. The coverage:diff script now matches them via the same dotfile
pattern used for .gitignore and .npmrc.

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

scripts/coverage/diff.mjs

@@ -47,6 +47,7 @@ const ALLOWED_GLOBS = [
   /\.ya?ml$/,
   /\.gitignore$/,
   /\.npmrc$/,
+  /(^|\/)\.env(\.[^/]+)?$/, // .env, .env.example, .env.local, etc.
   // Shell scripts (not Vitest-covered)
   /\.sh$/,
   /\.bash$/,

scripts/coverage/diff.test.mjs

@@ -154,6 +154,19 @@ describe("computeDiffCoverage", () => {
     assert.equal(result.summary.filesChanged, 4);
   });
 
+  test("skips .env template files (.env, .env.example, .env.local)", () => {
+    const lcov = parseLcov(lcovText);
+    const diff = new Map([
+      [".env.example", new Set([1, 2, 3])],
+      [".env.local", new Set([1])],
+      [".env", new Set([1])],
+    ]);
+    const result = computeDiffCoverage(diff, lcov);
+    assert.equal(result.status, "pass");
+    assert.equal(result.summary.filesGated, 0);
+    assert.equal(result.summary.filesChanged, 3);
+  });
+
   test("end-to-end fixture: mixed pass/fail/skip/no-data", () => {
     const lcov = parseLcov(lcovText);
     const diff = parseGitDiff(diffText);