test(player): use the existing frontend_test wiring for api.test.mjs

main already runs the player's static JS unit tests via `make
test-frontend` over pkg/service/soundtouchweb/frontend_test/*.test.mjs,
wired into .github/workflows/browser-tests.yml. That target was added by
PR #672 and this change predates it.

api.test.mjs was placed in static/js/ instead and run by a second `node
--test` invocation bolted onto test-browser, behind a new NODE variable.
That is a parallel test-wiring convention for one file, and it also mixes
a test into the directory that is served to browsers as static assets.

Move the file next to the other frontend tests and revert the Makefile
change; the existing target and CI job pick it up unchanged.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Makefile

@@ -11,7 +11,6 @@ GOTEST=$(GOCMD) test
 GOGET=$(GOCMD) get
 GOMOD=$(GOCMD) mod
 GOFMT=gofmt
-NODE?=node
 
 # Build parameters
 BINARY_NAME=soundtouch-cli
@@ -156,7 +155,6 @@ test-coverage:
 test-browser:
 	@echo "Running browser-level compatibility tests..."
 	$(GOTEST) -tags browsertest -v ./pkg/service/soundtouchweb/...
-	$(NODE) --test pkg/service/soundtouchweb/static/js/api.test.mjs
 
 # Unit tests for the embedded player's static JS modules (see
 # pkg/service/soundtouchweb/frontend_test/), run via Node's built-in test

pkg/service/soundtouchweb/frontend_test/api.test.mjs

@@ -1,7 +1,7 @@
 import assert from 'node:assert/strict';
 import test from 'node:test';
 
-import { api } from './api.js';
+import { api } from '../static/js/api.js';
 
 test('selectSource posts the exact source and account body', async () => {
     const requests = [];