Add comprehensive technical documentation for FPS Game project

[Copilot]

User requested detailed documentation of the project's technology stack and key code implementations for study purposes.

Changes

New Documentation

• TECH_STACK.md (42KB, 1,513 lines) - Comprehensive technical reference

  • Technology stack breakdown: Java 17, Maven multi-module, TCP sockets, Swing UI, JUnit 5
  • Module-by-module code analysis:
    • comfps-common: Protocol serialization, game enums, snapshot synchronization, character system
    • comfps-server: FSM game loop, TCP server, session management, message routing
    • comfps-client: Network client, snapshot interpolation, UI components
  • Network protocol specifications (12 opcodes with byte-level payload structures)
  • Game flow FSM (6-phase state machine with transition conditions)
  • Build/execution instructions with Maven commands

• STUDY_GUIDE.md (9.4KB) - Structured learning path

  • 7-phase study roadmap (~8 hours total)
  • Core concept summaries (architecture, protocol, FSM, interpolation)
  • Quick-start execution guide

Updated Files

• README.md - Added links to new technical docs, updated build commands to use Maven
• .gitignore - Excluded build artifacts (target/, *.class, *.jar)

Code Example

Network protocol frame structure documented with byte-level detail:

Frame: [4B: length] [1B: opcode] [N bytes: payload]

SNAPSHOT (0x31):
  [4B: playerCount]
  for each player:
    [4B: playerId] [4B: float x] [4B: float y] [4B: float aim]
    [1B: team] [1B: character]

Client-side interpolation algorithm:

// Buffer snapshots with timestamps
public void push(byte[] snapshotPayload, long recvNs);

// Sample at 100ms delay with linear interpolation
public Map<Integer, Entry> sample(long nowNs) {
    long targetNs = nowNs - interpDelayNs; // 100ms past
    // Find surrounding snapshots, lerp between them
}

Original prompt

우리 프로젝트에 대해 공부를 좀 하고싶은데 사용된 기술 스택과 주요한 코드에 대해서 정리하고 설명해줘 자세하게 전부 파악하고싶어

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