refactor(eslint): ban vi.mock('pdfjs-dist', ...) in spec/test files — ADR 012

Adds a no-restricted-syntax rule scoped to *.spec.ts / *.test.ts that
flags any vi.mock call whose first argument starts with 'pdfjs-dist'.
Turns the ~2-min CI wait into an immediate lint error on save.
Updates ADR 012 Enforcement section to document the rule.

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

frontend/eslint.config.js

@@ -72,6 +72,20 @@ export default defineConfig(
 			]
 		}
 	},
+	{
+		files: ['**/*.spec.ts', '**/*.test.ts'],
+		rules: {
+			'no-restricted-syntax': [
+				'error',
+				{
+					selector:
+						"CallExpression[callee.object.name='vi'][callee.property.name='mock'] > Literal[value=/^pdfjs-dist/]",
+					message:
+						"Banned: vi.mock('pdfjs-dist', factory) causes a birpc teardown race in browser-mode specs — see ADR 012. Use the libLoader prop injection pattern instead."
+				}
+			]
+		}
+	},
 	{
 		plugins: { boundaries },
 		settings: {