reorganize project structure and migrate source to src/

[hackerby888]

• Documentation: Moved .md files → doc/
• Configuration: Moved .conf files → conf/
• Scripts: Moved script files → scripts/
• Source Code: Migrated core source files to src/
• Modularity: Grouped related files into separate subdirectories for better organization.

Project structure

.
├── .github/workflows/
├── conf/
├── doc/
├── docker/
├── external/XKCP/
├── scripts/
├── src/
│   ├── connection/
│   ├── core/
│   ├── database/
│   ├── processors/
│   │   ├── indexer/
│   │   ├── io/
│   │   ├── logging/
│   │   └── ticking/
│   ├── rest_api/
│   └── utils/
├── tests/
├── web/
├── CMakeLists.txt
└── .clang-format