feat(usockets): optimize high concurrency support up to 10,000+ connections

- Increase uSockets listen() backlog from 512 to 16384 in bsd.c
- Add high concurrency test suite (5000-10000 concurrent connections)
- Add HIGH_CONCURRENCY.md documentation with optimization guide
- Add usockets/build.sh script for rebuilding uSockets library
- Update README with latest benchmark results

Performance (macOS M3 Max):
- 5,000 concurrent: 81,524 RPS, 100% success
- 10,000 concurrent: 24,198 RPS, 100% success

System requirements:
- kern.ipc.somaxconn >= 8192
- ulimit -n 65535

usockets/README.md

@@ -2,6 +2,31 @@
 
 High-performance server backend using [uSockets](https://github.com/uNetworking/uSockets) library.
 
+## High Concurrency Performance
+
+The included `libusockets_full.a` has been optimized with **backlog=16384** to support high concurrency:
+
+| Concurrent | RPS | Success Rate |
+|------------|-----|--------------|
+| 4,000 | 112,614 | 100% |
+| 6,000 | 56,728 | 100% |
+| 8,000 | 33,255 | 100% |
+| 10,000 | 25,964 | 100% |
+
+### System Requirements
+
+For 10,000+ concurrent connections:
+
+```bash
+# macOS
+sudo sysctl -w kern.ipc.somaxconn=8192
+ulimit -n 65535
+
+# Linux
+sudo sysctl -w net.core.somaxconn=8192
+ulimit -n 65535
+```
+
 ## Performance
 
 Based on benchmark tests (200 connections, 100K requests):