feat(frontend): add stations library reader with tdd

frontend/src/tests/fixtures/library/alpha/_meta.yml

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+name: Alpha
+description: alpha station
+color: '#ff0000'
+tags: [test, alpha]

frontend/src/tests/fixtures/library/bad-yaml/_meta.yml

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+name: "unterminated
+description: never closes

frontend/src/tests/fixtures/library/beta/_meta.yml

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+name: Beta
+description: beta station
+color: '#00ff00'
+tags: [test, beta]

frontend/src/tests/fixtures/library/beta/cover.jpg

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+fake cover

frontend/src/tests/stations.test.ts

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+import { describe, expect, it } from 'vitest';
+import path from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { listStations, readMeta } from '@lib/stations';
+
+const HERE = path.dirname(fileURLToPath(import.meta.url));
+const FIXTURES = path.resolve(HERE, 'fixtures/library');
+
+describe('readMeta', () => {
+  it('returns null for missing _meta.yml', async () => {
+    expect(await readMeta(FIXTURES, 'empty')).toBeNull();
+  });
+
+  it('returns null for malformed yaml (logged, not thrown)', async () => {
+    expect(await readMeta(FIXTURES, 'bad-yaml')).toBeNull();
+  });
+
+  it('returns null when the id has uppercase letters (regex rejection, no fs read)', async () => {
+    expect(await readMeta(FIXTURES, 'NotLower')).toBeNull();
+  });
+
+  it('parses a valid station', async () => {
+    const s = await readMeta(FIXTURES, 'alpha');
+    expect(s).toEqual({
+      id: 'alpha',
+      name: 'Alpha',
+      description: 'alpha station',
+      color: '#ff0000',
+      tags: ['test', 'alpha'],
+      mounts: { mp3: '/alpha.mp3', opus: '/alpha.opus' },
+      cover: null,
+    });
+  });
+
+  it('sets cover when a cover file exists', async () => {
+    const s = await readMeta(FIXTURES, 'beta');
+    expect(s?.cover).toBe('/api/stations/beta/cover');
+  });
+});
+
+describe('listStations', () => {
+  it('returns only valid stations, sorted by id', async () => {
+    const ss = await listStations(FIXTURES);
+    expect(ss.map((s) => s.id)).toEqual(['alpha', 'beta']);
+  });
+
+  it('skips empty and bad-yaml folders', async () => {
+    const ss = await listStations(FIXTURES);
+    expect(ss.find((s) => s.id === 'empty')).toBeUndefined();
+    expect(ss.find((s) => s.id === 'bad-yaml')).toBeUndefined();
+  });
+
+  it('handles a non-existent root gracefully', async () => {
+    expect(await listStations('/no/such/dir')).toEqual([]);
+  });
+});