fix(build): discover unit tests under server/, not only src/

npm test is the only suite CI runs, and its discovery walked src/ alone, so
server/providers/transitHistory.test.mjs has never executed since it was
added. Its 8 tests pass, so this was silent coverage loss rather than a hidden
failure: the file reads like covered code in review and never ran anywhere.

Add server/ to the searched roots, and pin the property with a test that walks
the repository itself and compares the two sets, so a tree added later without
updating the roots fails loudly instead of going quiet.

Suite goes from 5090 to 5099 tests, 0 failures: the 8 tests in that file plus
the regression test added here.

scripts/run-unit-tests.mjs

@@ -21,9 +21,19 @@ export function assertNode24AllocationRuntime(version = process.versions.node) {
   return version;
 }
 
+/**
+ * Directories this runner searches for `*.test.mjs`, in stable order.
+ *
+ * `server/` belongs here because provider modules own tests of their own: a
+ * suite placed beside the module it covers must run, and `npm test` is the only
+ * thing CI invokes, so a directory missing from this list is a suite that never
+ * runs anywhere. `unitTestRunner.test.mjs` asserts the list covers every test
+ * file in the repository, so adding a tree without adding it here fails.
+ */
+export const UNIT_TEST_ROOTS = Object.freeze(['src', 'server']);
+
 /** Discover repository unit tests in stable path order. */
 export function discoverUnitTestFiles(root = process.cwd()) {
-  const sourceRoot = path.join(root, 'src');
   const files = [];
   const visit = (directory) => {
     for (const entry of readdirSync(directory, { withFileTypes: true })) {
@@ -34,7 +44,7 @@ export function discoverUnitTestFiles(root = process.cwd()) {
       }
     }
   };
-  visit(sourceRoot);
+  for (const testRoot of UNIT_TEST_ROOTS) visit(path.join(root, testRoot));
   return files.sort();
 }