feat: add Netty and Java NIO interview questions

Added 3 comprehensive interview documents covering Netty and Java NIO:

**1. Netty Core Principles (Netty核心原理.md)**
- Core components: Channel, EventLoop, ChannelPipeline, ByteBuf
- Reactor threading model (single/multi-threaded, master-slave)
- ByteBuf vs Java NIO ByteBuffer
- Zero-copy implementation (4 approaches)
- ChannelPipeline and ChannelHandler
- TCP sticky/unpacking problem solutions
- Heartbeat mechanism

**2. Java NIO Core Principles (Java NIO核心原理.md)**
- NIO vs BIO comparison
- Three core components: Channel, Buffer, Selector
- Selector multiplexing mechanism
- Channel vs Stream differences
- Buffer core attributes and usage
- Non-blocking I/O implementation
- Zero-copy with transferTo and MappedByteBuffer

**3. Netty Practice Scenarios (Netty实战场景.md)**
- High-performance RPC framework design
- WebSocket server implementation
- Million-connection IM system architecture
- Memory leak detection and resolution
- Graceful shutdown implementation
- Heartbeat and reconnection mechanisms

Each document includes:
- Detailed problem descriptions
- Complete code examples (Java)
- Architecture diagrams
- Best practices
- Performance optimization tips
- P7-level bonus points

Total: 3 documents, covering:
- Theoretical foundations
- Practical implementations
- Production scenarios
- Performance tuning
- Common pitfalls

Suitable for backend P7 interview preparation.

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

.obsidian/workspace.json

@@ -196,6 +196,9 @@
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