Add HTTP range request support for video streaming

Safari and other browsers require Accept-Ranges: bytes and 206 Partial
Content responses to play video. Without this, large videos fail to load
(especially in Safari) because the entire file had to buffer in memory
before sending.

- Replace readFile + Buffer with createReadStream for efficient streaming
- Parse Range header (start-end, start-, and suffix -N forms)
- Return 206 Partial Content with Content-Range for range requests
- Return 416 Range Not Satisfiable for out-of-bounds ranges
- Add Accept-Ranges: bytes to all raw file responses

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

tests/integration/pages.test.ts

@@ -125,6 +125,51 @@ describe('GET /f/:id and GET /f/:id/raw', () => {
     const res = await ctx.app.inject({ method: 'GET', url: `/f/${fileId}/raw` });
     expect(res.statusCode).toBe(200);
     expect(res.body).toBe('hello!');
+    expect(res.headers['accept-ranges']).toBe('bytes');
+  });
+
+  it('returns 206 for a byte range request', async () => {
+    const res = await ctx.app.inject({
+      method: 'GET',
+      url: `/f/${fileId}/raw`,
+      headers: { range: 'bytes=0-3' },
+    });
+    expect(res.statusCode).toBe(206);
+    expect(res.headers['content-range']).toBe('bytes 0-3/6');
+    expect(res.headers['content-length']).toBe('4');
+    expect(res.body).toBe('hell');
+  });
+
+  it('returns 206 for an open-ended range request', async () => {
+    const res = await ctx.app.inject({
+      method: 'GET',
+      url: `/f/${fileId}/raw`,
+      headers: { range: 'bytes=2-' },
+    });
+    expect(res.statusCode).toBe(206);
+    expect(res.headers['content-range']).toBe('bytes 2-5/6');
+    expect(res.body).toBe('llo!');
+  });
+
+  it('returns 206 for a suffix range request', async () => {
+    const res = await ctx.app.inject({
+      method: 'GET',
+      url: `/f/${fileId}/raw`,
+      headers: { range: 'bytes=-3' },
+    });
+    expect(res.statusCode).toBe(206);
+    expect(res.headers['content-range']).toBe('bytes 3-5/6');
+    expect(res.body).toBe('lo!');
+  });
+
+  it('returns 416 for an unsatisfiable range', async () => {
+    const res = await ctx.app.inject({
+      method: 'GET',
+      url: `/f/${fileId}/raw`,
+      headers: { range: 'bytes=100-200' },
+    });
+    expect(res.statusCode).toBe(416);
+    expect(res.headers['content-range']).toBe('bytes */6');
   });
 
   it('returns 404 for unknown file', async () => {