Add project directory guide to Contributing page

Annotated tree of the Erupe directory structure showing what each
directory and key file does, with pointers for common tasks (features,
bugs, DB changes, binary formats).

Closes Mezeporta/Erupe#47

Contributing.md

@@ -2,6 +2,84 @@
 
 This guide covers the development workflows for working on the Erupe codebase.
 
+## Project Directory Guide
+
+```
+Erupe/
+├── main.go                  # Entry point — starts all servers, handles shutdown
+├── config.example.json      # Template config (copy to config.json)
+│
+├── config/                  # Config loading (Viper-backed)
+│   └── config.go            #   Main Config struct, game version modes (S1–ZZ)
+│
+├── network/                 # Protocol layer
+│   ├── packetid.go          #   Packet ID enum (~200+ opcodes, `go generate` for stringer)
+│   ├── crypt_conn.go        #   Blowfish-encrypted TCP connection
+│   ├── crypt_packet.go      #   Packet framing and checksum
+│   ├── mhfpacket/           #   ~400 packet structs (one file per message type)
+│   │   └── msg_mhf_*.go     #     Parse/Build for each packet
+│   ├── binpacket/           #   Binary relay packets (chat, mail, targeted)
+│   ├── crypto/              #   Low-level Blowfish cipher
+│   └── clientctx/           #   Per-connection context
+│
+├── server/
+│   ├── channelserver/       # Gameplay server (by far the largest)
+│   │   ├── handlers_table.go    # PacketID → handler dispatch (~200 entries)
+│   │   ├── handlers_quest.go    # Quest system
+│   │   ├── handlers_guild.go    # Guild operations (14 tables)
+│   │   ├── handlers_stage.go    # Multiplayer rooms/lobbies
+│   │   ├── handlers_cast_binary.go  # Real-time state relay (position, animation)
+│   │   ├── handlers_mail.go     # In-game mail
+│   │   ├── handlers_shop.go     # Shops and gacha
+│   │   ├── handlers_*.go        # ... ~50 handler files by game system
+│   │   ├── sys_session.go       # Per-connection state (character, stage, send queue)
+│   │   ├── sys_stage.go         # Stage lifecycle, player sync
+│   │   ├── sys_semaphore.go     # Distributed locks (Raviente, guild ops)
+│   │   ├── sys_channel_server.go    # Server lifecycle, Raviente shared state
+│   │   └── compression/         # Save data compression
+│   ├── signserver/          # Authentication (TCP 53312)
+│   ├── entranceserver/      # World list & character select (TCP 53310)
+│   ├── api/                 # REST API (port 8080) — launcher, screenshots
+│   └── discordbot/          # Discord bot — slash commands, chat relay
+│
+├── common/                  # Shared utility libraries
+│   ├── byteframe/           #   Binary read/write (big-endian)
+│   ├── bfutil/              #   Blowfish helpers
+│   ├── decryption/          #   Game file decryption
+│   ├── gametime/            #   MHF time ↔ real time conversion
+│   ├── mhfcourse/           #   Course/subscription definitions
+│   ├── mhfitem/             #   Item ID lookups
+│   ├── mhfmon/              #   Monster ID lookups
+│   ├── mhfcid/              #   Character ID handling
+│   ├── token/               #   Session token generation
+│   ├── pascalstring/        #   Length-prefixed string parsing
+│   ├── stringstack/         #   Stack for stage movement history
+│   └── stringsupport/       #   String utilities
+│
+├── schemas/                 # PostgreSQL schema management
+│   ├── init.sql             #   Base schema (pg_dump format, bootstraps to v9.1.0)
+│   ├── patch-schema/        #   Incremental dev patches (apply in order)
+│   ├── update-schema/       #   Consolidated release schemas
+│   └── bundled-schema/      #   Demo data (shops, events, gacha)
+│
+├── bin/                     # Game data files (served to clients)
+│   ├── quests/              #   Quest binaries
+│   ├── scenarios/           #   Cutscene/scenario files
+│   └── events/              #   Event quest archives
+│
+├── docker/                  # Docker Compose setup (PostgreSQL, pgAdmin, server)
+├── tools/loganalyzer/       # Log analysis utility
+├── vendor/                  # Vendored Go dependencies
+└── .github/                 # CI workflows (test, race, coverage, build)
+```
+
+### Where to look first
+
+- **Implementing a feature?** Start with the `handlers_*.go` file for that game system, then check the packet structs in `network/mhfpacket/`.
+- **Fixing a bug?** Enable packet logging (see [Debugging](#debugging)) and trace from `handlers_table.go` to the relevant handler.
+- **Adding a DB table?** Create a new patch in `schemas/patch-schema/` with the next number in sequence.
+- **Understanding binary formats?** `common/byteframe/` is the serialization layer used everywhere.
+
 ## Adding a Packet Handler
 
 This is the most common type of contribution. A new packet handler touches 4 files and optionally a 5th for code generation.