Docs: add the language servers missing from the supported-language lists

Several backends that are registered and tested were absent from the
user-facing lists: six from the README (pascal, qml, rego, systemverilog,
terraform, vue), six from the Language Support docs page (matlab,
powershell, rego, systemverilog, terraform, toml), and two from the
commented language-server list in the project template
(python_basedpyright, qml).

The drift is long-standing and runs in both directions: matlab,
powershell and toml reached the README but never the docs page; pascal,
vue and qml reached the docs page but never the README; terraform, rego
and systemverilog reached neither, the oldest of them since 2025-07-06.
The two template omissions are the most recent, from #1705 and #1635.
The guide's Documentation step does ask for the README and the docs page,
so most of this was missed rather than unspecified; it does not mention
the project template at all.

The setup notes on the new docs-page entries name the versions Serena
actually pins, taken from the corresponding language-server modules:
MATLAB extension 1.3.9, PowerShell Editor Services 4.4.0 and
PSScriptAnalyzer 1.25.0, Verible v0.0-4051-g9fdb4057, terraform-ls
0.36.5, and Taplo 0.10.0. The PowerShell entry mentions both automatic
installations, since enabling that backend also runs Save-Module against
the user's configured PowerShell repository.

The new Regal link points at open-policy-agent/regal, the current
canonical repository; StyraInc/regal still redirects there, and the
adapter and the CI workflow have not been changed.

The template block is refreshed from scripts/print_language_list.py,
which is why its column widths change: python_basedpyright is longer than
any identifier the previous list contained. The pointer directly below it
still named the Language enum, renamed to LanguageServerId in d2cf18dd.

README.md

@@ -110,7 +110,7 @@ Serena incorporates a powerful abstraction layer for the integration of language
 The underlying language servers are typically open-source projects or at least freely available for use.
 
 When using Serena's language server backend, we provide **support for over 40 programming languages**, including
-Ada / SPARK, AL, Angular, Ansible, Bash, BSL, C#, C/C++, Clojure, Crystal, CUE, Dart, Elixir, Elm, Erlang, Fortran, F#, GDScript, GLSL, Go, Groovy, Haskell, Haxe, HLSL, HTML, Java, JavaScript, JSON, Julia, Kotlin, LaTeX, Lean 4, Lua, Luau, Markdown, MATLAB, mSL, Nix, OCaml, Perl, PHP, PowerShell, Python, R, Ruby, Rust, Scala, SCSS / Sass / CSS, Solidity, Svelte, Swift, TOML, TypeScript, WGSL, YAML, and Zig.
+Ada / SPARK, AL, Angular, Ansible, Bash, BSL, C#, C/C++, Clojure, Crystal, CUE, Dart, Elixir, Elm, Erlang, Fortran, F#, GDScript, GLSL, Go, Groovy, Haskell, Haxe, HLSL, HTML, Java, JavaScript, JSON, Julia, Kotlin, LaTeX, Lean 4, Lua, Luau, Markdown, MATLAB, mSL, Nix, OCaml, Pascal, Perl, PHP, PowerShell, Python, QML, R, Rego, Ruby, Rust, Scala, SCSS / Sass / CSS, Solidity, Svelte, Swift, SystemVerilog, Terraform, TOML, TypeScript, Vue, WGSL, YAML, and Zig.
 
 ### The Serena JetBrains Plugin