Tighten the linguist override regression so contradictions fail

The first pass only checked substring presence, which meant the test could stay
green even if conflicting `.gitattributes` rules were added later. This switches
that guardrail to an exact normalized line match for the override block.

Constraint: Keep the fix scoped to the single actionable CodeRabbit finding on PR #389
Rejected: Add broader parser helpers or extra metadata tests | unnecessary for a five-line override contract
Confidence: high
Scope-risk: narrow
Directive: Keep this assertion exact; if the override block changes, update the expected normalized lines in one place
Tested: `npm test -- test/documentation.test.ts`; `npm run lint`; `npm run typecheck`
Not-tested: Full `npm test` remains red on inherited `test/proactive-refresh.test.ts` timeouts reproduced earlier on clean `origin/main`

Author: ndycode

test/documentation.test.ts

@@ -617,11 +617,17 @@ function compareSemverDescending(left: string, right: string): number {
 		).toBe(true);
 
 		const content = read(gitattributes);
-		expect(content).toContain("*.ts linguist-detectable");
-		expect(content).toContain("*.js -linguist-detectable");
-		expect(content).toContain("*.mjs -linguist-detectable");
-		expect(content).toContain("*.sh -linguist-detectable");
-		expect(content).toContain("*.html -linguist-detectable");
+		const normalized = content
+			.split(/\r?\n/)
+			.map((line) => line.trim())
+			.filter((line) => line.length > 0 && !line.startsWith("#"));
+		expect(normalized).toEqual([
+			"*.ts linguist-detectable",
+			"*.js -linguist-detectable",
+			"*.mjs -linguist-detectable",
+			"*.sh -linguist-detectable",
+			"*.html -linguist-detectable",
+		]);
 	});
 
 	it("publishes maintainer runbooks for refactor-era changes", () => {