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.

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

@@ -109,6 +109,8 @@ Some languages require additional installations or setup steps, as noted.
 * **Luau**
 * **Markdown**  
   (must explicitly enable language `markdown`, primarily useful for documentation-heavy projects)
+* **MATLAB**  
+  (requires Node.js and a licensed local MATLAB installation, R2021b or later; Serena automatically downloads version 1.3.9 of the VS Code MATLAB extension, which bundles the language server)
 * **mSL** (mIRC Scripting Language)  
   (auto-installed; no external dependencies required — uses a custom pygls-based LSP server shipped with Serena;
   supports document symbols, workspace symbols, references, and go-to-definition for aliases, events, menus, dialogs, and CTCP handlers in `.mrc` files)
@@ -124,6 +126,8 @@ Some languages require additional installations or setup steps, as noted.
   (by default, uses the Intelephense language server (language `php`), set `INTELEPHENSE_LICENSE_KEY` environment variable for premium features;
   we also support [Phpactor](https://github.com/phpactor/phpactor) (language `php_phpactor`), which requires PHP 8.1+;
   and the experimental [PHPantom](https://github.com/PHPantom-dev/phpantom_lsp) backend (language `php_phpantom`)
+* **PowerShell**  
+  (requires PowerShell 7+ (`pwsh`) on PATH or in a standard install location; Serena automatically downloads PowerShell Editor Services 4.4.0 and installs PSScriptAnalyzer 1.25.0 via `Save-Module` from your configured PowerShell repository)
 * **Python**
   (by default, uses [Pyright](https://github.com/microsoft/pyright) (language `python`);
   alternatives: [BasedPyright](https://github.com/DetachHead/basedpyright) (language `python_basedpyright`),
@@ -135,6 +139,8 @@ Some languages require additional installations or setup steps, as noted.
   (requires Qt 6, provides `qmlls` or `qmlls6` on PATH; see the [Qt qmlls documentation](https://doc.qt.io/qt-6/qtqml-tool-qmlls.html))
 * **R**  
   (requires installation of the `languageserver` R package)
+* **Rego**  
+  (requires the [Regal](https://github.com/open-policy-agent/regal) language server on PATH)
 * **Ruby**  
   (by default, uses [ruby-lsp](https://github.com/Shopify/ruby-lsp) (language `ruby`); use language `ruby_solargraph` to use Solargraph instead.)
 * **Rust**  
@@ -150,6 +156,12 @@ Some languages require additional installations or setup steps, as noted.
 * **Svelte**
   (requires Node.js v18+ and npm; supports `.svelte` Single File Components plus TypeScript/JavaScript files via `svelte-language-server`; a companion `typescript-language-server` + `typescript-svelte-plugin` is spawned automatically for cross-file rename, go-to-definition, and references across `.ts`/`.js` and `.svelte` files; use language `svelte` for Svelte projects instead of also enabling `typescript`)
 * **Swift**
+* **SystemVerilog**  
+  (uses `verible-verilog-ls`, taken from PATH if present, otherwise version `v0.0-4051-g9fdb4057` is downloaded automatically)
+* **Terraform**  
+  (uses `terraform-ls` 0.36.5, which Serena downloads automatically; requires Terraform on PATH)
+* **TOML**  
+  (experimental; uses Taplo 0.10.0, taken from PATH if present, otherwise downloaded automatically)
 * **TypeScript**
 * **Vue**    
   (3.x with TypeScript; requires Node.js v18+ and npm; supports .vue Single File Components with monorepo detection)