feat: add GDScript (Godot Engine) language server support

Closes #1446. Adds Language.GDSCRIPT backed by a new TCPLanguageServer
that extends LanguageServerInterface directly — no intermediate transport
abstraction layer.

Changes:
- ls_process.py: adds TCPConnectionInfo dataclass and TCPLanguageServer,
  a LanguageServerInterface subclass that manages a TCP socket directly
  (mirroring how StdioLanguageServer manages a subprocess). Stop order
  closes the socket before the BufferedReader wrapper to avoid a deadlock
  where BufferedReader.close() blocks on its internal read lock while
  readline() holds it waiting for data.
- ls_config.py: adds Language.GDSCRIPT with .gd/.gdscript file matcher.
- language_servers/godot_language_server.py: GodotLanguageServer connects
  to the Godot editor's TCP LSP (port 6008, same for Godot 3 and 4),
  registers Godot-specific notification handlers, and performs the
  initialize/initialized handshake. Godot version is auto-detected from
  config_version in project.godot.
- docs: adds GDScript to the language support list and a dedicated setup
  guide covering prerequisites, setup steps, performance characteristics
  (no workspace/symbol support → first full scan is slow, disk cache
  persists across sessions), and known limitations.

Tested against Godot 4.6.1 on Linux (Fedora 41): TCP connection,
initialize handshake, textDocument/documentSymbol returning full symbol
tree, and clean shutdown in <1s.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

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

@@ -71,6 +71,10 @@ Some languages require additional installations or setup steps, as noted.
   (requires [.NET v8.0+](https://dotnet.microsoft.com/en-us/download/dotnet); uses FsAutoComplete/Ionide, which is auto-installed; for Homebrew .NET on macOS, set DOTNET_ROOT in your environment)
 * **Fortran**   
   (requires installation of fortls: `pip install fortls`)
+* **GDScript** (Godot Engine)  
+  (requires the Godot editor to be running with its built-in LSP enabled — default on port 6008;
+  Serena connects over TCP and does not launch Godot itself;
+  see the [GDScript Setup Guide](../03-special-guides/godot_gdscript_setup_guide_for_serena) for details)
 * **Go**  
   (requires installation of `gopls`)
 * **Groovy**