feat: add JSON language server support via vscode-json-languageserver (#1404)

* feat: add JSON language server support via vscode-json-languageserver (fixes #1391)

Add support for JSON files using the `vscode-json-languageserver` npm package
from Microsoft. This provides document symbol navigation and hover information
for JSON files.

The implementation follows the existing YAML language server pattern:
- Auto-installs `vscode-json-languageserver` via npm on first use
- Requires Node.js and npm
- Marked as experimental (must be explicitly specified)

Co-Authored-By: Octopus <liyuan851277048@icloud.com>
Co-authored-by: octo-patch <octo-patch@github.com>
Co-authored-by: Michael Panchenko <35432522+MischaPanch@users.noreply.github.com>

docs/01-about/020_programming-languages.md

@@ -115,6 +115,8 @@ Some languages require additional installations or setup steps, as noted.
 * **Vue**    
   (3.x with TypeScript; requires Node.js v18+ and npm; supports .vue Single File Components with monorepo detection)
 * **YAML**
+* **JSON**  
+  (experimental; must be explicitly added to the languages list; requires Node.js and npm)
 * **Zig**  
   (requires installation of ZLS - Zig Language Server)