docs: enhance documentation structure and clarify repository layout

- Updated the README and various documentation files to reflect the new flat layout of the `gregFramework`, emphasizing the direct placement of repositories like `gregMod.<Name>/` and `gregExt.<Name>/` under `gregFramework/`.
- Added details about the `gregModmanager/` and `gregDataCenterExporter/` directories, clarifying their roles and contents.
- Improved descriptions and links throughout the documentation to ensure consistency and accuracy, enhancing user navigation and understanding of the project structure.
- Adjusted language in several sections to better communicate the purpose and organization of the repositories.

This commit improves the overall clarity and usability of the documentation.

docs/reference/modding-language-requirement.md

@@ -20,7 +20,7 @@ That applies to anything shipped as a **`gregMod.*`**, **`gregExt.*`**, or **`FF
 
 ## What this does *not* restrict
 
-- **Framework core** (`gregCore`) may still contain **non-C#** components maintained by core maintainers (for example the **Rust** FFI bridge under `bridges/gregSta.RustBridge/`, build scripts, or tooling). Those are **not** substitutes for implementing mod/plugin/extension behavior outside C#.
+- **Framework core** (`gregCore`) may still contain **non-C#** components maintained by core maintainers (for example the **Rust** FFI bridge under `gregCore/bridges/gregSta.RustBridge/`, build scripts, or tooling). Those are **not** substitutes for implementing mod/plugin/extension behavior outside C#.
 - **Documentation**, **config** (JSON/YAML), and **assets** are not “logic” in this sense.
 - **gregStore**, **gregWiki**, and other non–in-game stacks may use other languages as appropriate.