feat: upgrade to gnome 51

Adds GNOME Shell 51 to shell-version and moves the build onto the
GNOME 51 type packages.

- tabBar: pass orientation instead of vertical to St.BoxLayout. The vertical
  property was removed from St widgets in 51 (deprecated in 48); orientation
  exists in 48 and later, so this keeps 48-51 working. Verified against the
  installed St-51 typelib
- switch to @girs/gjs 5.5.0 and the -51 namespace packages (shell/st/meta/
  clutter plus gio/glib/gobject/gtk/gdk/adw/pango)
- drop @girs/gnome-shell 50 and the stale @girs/mtk-17 dependency. The
  umbrella is GNOME 50 only and pulls St-18 and Meta-18 types that clash
  with the -51 packages
- types/: hand-written declarations for the Shell JS modules imported here
  (extension.js, prefs.js, main.js). Upstream 51 types (51.0.0-alpha.1) are
  not published to npm yet
- TypeScript 6.0.3 rather than 7: typescript-eslint requires <6.1.0 and
  ts-jest requires <7
- eslint 10.12, @eslint/js 10.0.1, eslint-plugin-jsdoc 65.3.4,
  typescript-eslint 8.71.2 and jest 30.5.2 / ts-jest 29.4.14

types/shell-globals.d.ts

@@ -0,0 +1,20 @@
+/**
+ * GNOME Shell runtime globals.
+ *
+ * The `global` object is created by the shell before an extension is loaded and
+ * has no `.gir`, so it is not covered by the generated `@girs/*-51` packages.
+ * Upstream ships these in `@girs/gnome-shell`, but its GNOME 51 build
+ * (51.0.0-alpha.1) is unpublished, and v50 pulls St-18/Meta-18 types that
+ * collide with the -51 packages. Declaring the few symbols we use keeps the
+ * project on GNOME 51 types and installable from the registry.
+ *
+ * @see https://gitlab.gnome.org/GNOME/gnome-shell/-/blob/main/js/ui/environment.js
+ */
+import type Shell from "@girs/shell-51";
+
+declare global {
+    /** Global shell object created by GNOME Shell on startup. */
+    const global: Shell.Global;
+}
+
+export {};

types/shell-modules.d.ts

@@ -0,0 +1,131 @@
+/**
+ * Ambient declarations for the GNOME Shell JavaScript modules this extension
+ * imports.
+ *
+ * Shell's JavaScript API has no `.gir`, so generated `@girs/*` types do not
+ * cover it. Upstream maintains those types in `@girs/gnome-shell`, but its
+ * GNOME 51 support (51.0.0-alpha.1) is unpublished on npm, and v50 depends on
+ * St-18/Meta-18 types that conflict with the -51 packages this project uses.
+ * Only the symbols actually imported here are declared; extend as needed.
+ *
+ * @see https://gitlab.gnome.org/GNOME/gnome-shell/-/tree/main/js/ui
+ */
+
+declare module "resource:///org/gnome/shell/extensions/extension.js" {
+    import type Gio from "@girs/gio-2.0";
+
+    /** Parsed contents of the extension's `metadata.json`. */
+    export interface ExtensionMetadata {
+        uuid: string;
+        name: string;
+        description: string;
+        "shell-version"?: string[];
+        "settings-schema"?: string;
+        "gettext-domain"?: string;
+        url?: string;
+        [key: string]: unknown;
+    }
+
+    /**
+     * Base class for an extension's `extension.js` default export.
+     *
+     * GNOME Shell 51 requires `disable()` to stay synchronous; returning a
+     * promise now throws.
+     */
+    export class Extension {
+        constructor(metadata: ExtensionMetadata);
+
+        readonly metadata: ExtensionMetadata;
+        readonly uuid: string;
+        readonly path: string;
+
+        /** Returns a {@link Gio.Settings} for the extension's schema. */
+        getSettings(schema?: string | null, subdir?: string | null): Gio.Settings;
+
+        /** Marks the extension's settings as translatable. */
+        translateConfig(): void;
+
+        /** Opens the extension's preferences dialog, if it has one. */
+        openPreferences(): void;
+
+        enable(): void;
+        disable(): void;
+    }
+}
+
+declare module "resource:///org/gnome/Shell/Extensions/js/extensions/prefs.js" {
+    import type Gio from "@girs/gio-2.0";
+    import type Adw from "@girs/adw-1";
+
+    /** Marks a string for translation and returns the translation. */
+    export function gettext(str: string): string;
+
+    /** Pluralised form of {@link gettext}. */
+    export function ngettext(fid: string, fidPlural: string, n: number): string;
+
+    /** Context-sensitive form of {@link gettext}. */
+    export function pgettext(context: string, str: string): string;
+
+    /** Base class for an extension's `prefs.js` default export. */
+    export class ExtensionPreferences {
+        readonly metadata: Record<string, unknown>;
+        readonly uuid: string;
+        readonly path: string;
+
+        /** Returns a {@link Gio.Settings} for the extension's schema. */
+        getSettings(schema?: string | null, subdir?: string | null): Gio.Settings;
+
+        /** Marks the extension's settings as translatable. */
+        translateConfig(): void;
+
+        /** Called by the shell to populate the preferences window. */
+        fillPreferencesWindow(window: Adw.PreferencesWindow): Promise<void> | void;
+    }
+}
+
+declare module "resource:///org/gnome/shell/ui/main.js" {
+    import type Gio from "@girs/gio-2.0";
+    import type Meta from "@girs/meta-51";
+    import type Shell from "@girs/shell-51";
+    import type St from "@girs/st-51";
+
+    /** Window management helpers exposed to extensions. */
+    export interface ShellWM {
+        /**
+         * Registers a keybinding from an extension's schema and returns its id.
+         */
+        addKeybinding(
+            name: string,
+            settings: Gio.Settings,
+            flags: Meta.KeyBindingFlags,
+            mode: Shell.ActionMode,
+            handler: () => void,
+        ): number;
+
+        /** Removes a keybinding previously added by this extension. */
+        removeKeybinding(name: string): boolean;
+    }
+
+    /** The shell's layout manager. */
+    export interface LayoutManager {
+        /** Actor holding all non-window UI. */
+        readonly uiGroup: St.Widget;
+        /** Actor holding the window group. */
+        readonly windowGroup: St.Widget;
+        readonly panelBox: St.BoxLayout;
+        readonly monitorManager: Meta.MonitorManager;
+        readonly nMonitors: number;
+    }
+
+    /** The overview (window overview + search). */
+    export interface Overview extends St.Widget {
+        connect(signal: "showing" | "hiding" | "show-overview", callback: () => void): number;
+    }
+
+    export const wm: ShellWM;
+    export const layoutManager: LayoutManager;
+    export const overview: Overview;
+
+    /** Shows a notification in the message tray. */
+    export function notify(message: string): void;
+}