test: add middleware tests for auth, compression, and usage

- auth.test.ts (8 tests): missing key, Bearer/X-API-Key/query extraction, priority, invalid key, apiKeyInfo attachment
- compression.test.ts (5 tests): gzip for text/json, skip for images/small/no-accept
- usage.test.ts (7 tests): no keyInfo passthrough, tracking with headers, increment, 429 on limit, month reset, DB load, error handling

Total: 20 new tests, 205 passing (was 190)

src/middleware/__tests__/compression.test.ts

@@ -0,0 +1,65 @@
+import { describe, it, expect } from 'vitest'
+import express from 'express'
+import request from 'supertest'
+import { compressionMiddleware } from '../compression.js'
+
+function createApp() {
+  const app = express()
+  app.use(compressionMiddleware)
+
+  app.get('/text', (_req, res) => {
+    // Send enough data to exceed 1024 byte threshold
+    res.type('text/html').send('x'.repeat(2000))
+  })
+
+  app.get('/small', (_req, res) => {
+    res.type('text/html').send('small')
+  })
+
+  app.get('/image', (_req, res) => {
+    res.type('image/png').send(Buffer.alloc(2000))
+  })
+
+  app.get('/json', (_req, res) => {
+    res.type('application/json').send(JSON.stringify({ data: 'y'.repeat(2000) }))
+  })
+
+  return app
+}
+
+describe('compressionMiddleware', () => {
+  it('compresses text responses above threshold', async () => {
+    const res = await request(createApp())
+      .get('/text')
+      .set('Accept-Encoding', 'gzip')
+    expect(res.headers['content-encoding']).toBe('gzip')
+  })
+
+  it('does not compress responses below threshold', async () => {
+    const res = await request(createApp())
+      .get('/small')
+      .set('Accept-Encoding', 'gzip')
+    expect(res.headers['content-encoding']).toBeUndefined()
+  })
+
+  it('does not compress image responses', async () => {
+    const res = await request(createApp())
+      .get('/image')
+      .set('Accept-Encoding', 'gzip')
+    expect(res.headers['content-encoding']).toBeUndefined()
+  })
+
+  it('compresses JSON responses above threshold', async () => {
+    const res = await request(createApp())
+      .get('/json')
+      .set('Accept-Encoding', 'gzip')
+    expect(res.headers['content-encoding']).toBe('gzip')
+  })
+
+  it('does not compress when client does not accept gzip', async () => {
+    const res = await request(createApp())
+      .get('/text')
+      .set('Accept-Encoding', 'identity')
+    expect(res.headers['content-encoding']).toBeUndefined()
+  })
+})