feat: proxy POST /model/unload endpoint

- Add unloadModel() to whisper.ts: POSTs to /model/unload with 10s
  timeout, returns parsed JSON body, throws on non-ok response
- Create src/routes/api/model/unload/+server.ts: thin POST proxy,
  passes whisper's response through, returns 502 if whisper unreachable
- Add 3 unloadModel tests (success, WHISPER_URL config, error propagation)
  — 147/147 passing

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

src/tests/whisper.test.ts

@@ -21,7 +21,7 @@ vi.mock('form-data', () => ({
 
 vi.mock('fs', () => ({ createReadStream: vi.fn(() => 'STREAM_PLACEHOLDER') }));
 
-import { submitJob, streamJob, getModelStatus, cancelJob } from '$lib/server/whisper.js';
+import { submitJob, streamJob, getModelStatus, cancelJob, unloadModel } from '$lib/server/whisper.js';
 
 afterEach(() => vi.clearAllMocks());
 
@@ -341,6 +341,42 @@ describe('submitJob — SSE-triggered retry', () => {
 	});
 });
 
+// ── unloadModel ───────────────────────────────────────────────────────────────
+
+describe('unloadModel', () => {
+	it('POSTs to /model/unload and returns parsed body', async () => {
+		mocks.fetch.mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve({ ok: true })
+		});
+		const result = await unloadModel();
+		expect(result).toEqual({ ok: true });
+		expect(mocks.fetch).toHaveBeenCalledWith(
+			expect.stringContaining('/model/unload'),
+			expect.objectContaining({ method: 'POST' })
+		);
+	});
+
+	it('uses the configured WHISPER_URL', async () => {
+		vi.stubEnv('WHISPER_URL', 'http://gpu-box:9090');
+		mocks.fetch.mockResolvedValue({
+			ok: true,
+			json: () => Promise.resolve({ ok: true })
+		});
+		await unloadModel();
+		expect(mocks.fetch).toHaveBeenCalledWith(
+			'http://gpu-box:9090/model/unload',
+			expect.anything()
+		);
+		vi.unstubAllEnvs();
+	});
+
+	it('throws when whisper returns a non-ok response', async () => {
+		mocks.fetch.mockResolvedValue({ ok: false, status: 409 });
+		await expect(unloadModel()).rejects.toThrow('/model/unload');
+	});
+});
+
 // ── cancelJob ─────────────────────────────────────────────────────────────────
 
 describe('cancelJob', () => {