feat: Implement Plugin Marketplace Manager and Client

- Added PluginMarketplaceManager to coordinate marketplace reads and manage installed plugins.
- Introduced PluginMarketplaceClient for fetching marketplace metadata.
- Implemented storage management for installed plugins using MemoryStorage.
- Added methods for installing, uninstalling, and enabling/disabling plugins.
- Created type definitions for PluginMarketplaceManager options and installed plugin records.
- Added support for fetching full marketplace catalog and individual plugin metadata.
- Included error handling for fetch operations and validation of plugin data.
- Updated index.browser.ts to export new modules and types.

dist/PluginMarketplaceManager.d.ts

@@ -0,0 +1,88 @@
+import { type IPluginStorage } from './interfaces.js';
+import type { PluginRegistry } from './PluginRegistry.js';
+import type { InstalledPlugin, PluginMetadata } from './types.js';
+import { PluginMarketplaceClient } from './PluginMarketplaceClient.js';
+/**
+ * Host-visible installed-plugin metadata.
+ *
+ * Hosts may only know filesystem facts such as `id`, `name`, or `installedDate`.
+ * Stored marketplace metadata fills remaining fields.
+ */
+export type PluginMarketplaceInstalledRecord = Partial<InstalledPlugin> & Pick<InstalledPlugin, 'id'>;
+/**
+ * Host callbacks used by {@link PluginMarketplaceManager}.
+ */
+export interface PluginMarketplaceHostAdapter {
+    /**
+     * Returns host-known installed plugins.
+     */
+    listInstalledPlugins?(): Promise<PluginMarketplaceInstalledRecord[]>;
+    /**
+     * Performs host-specific install side effects.
+     */
+    installPlugin?(plugin: PluginMetadata): Promise<void>;
+    /**
+     * Performs host-specific uninstall side effects.
+     */
+    uninstallPlugin?(pluginId: string): Promise<void>;
+}
+/**
+ * Construction options for {@link PluginMarketplaceManager}.
+ */
+export interface PluginMarketplaceManagerOptions {
+    /** Shared marketplace client used to query remote metadata. */
+    client: PluginMarketplaceClient;
+    /** Optional persistent storage for installed-plugin state. */
+    storage?: IPluginStorage;
+    /** Optional host adapter for install and discovery side effects. */
+    host?: PluginMarketplaceHostAdapter;
+    /** Optional registry used when disabling or uninstalling loaded plugins. */
+    registry?: PluginRegistry;
+    /** Optional override for installed-plugin storage key. */
+    installedPluginsStorageKey?: string;
+}
+/**
+ * Coordinates marketplace reads with host-specific install and enable state.
+ */
+export declare class PluginMarketplaceManager {
+    private readonly client;
+    private readonly storage;
+    private readonly host?;
+    private readonly registry?;
+    private readonly installedPluginsStorageKey;
+    constructor(options: PluginMarketplaceManagerOptions);
+    /**
+     * Fetches full marketplace catalog.
+     */
+    fetchMarketplacePlugins(): Promise<PluginMetadata[]>;
+    /**
+     * Lists installed plugins merged with persisted enabled state.
+     */
+    listInstalledPlugins(): Promise<InstalledPlugin[]>;
+    /**
+     * Lists installed plugins currently enabled.
+     */
+    listEnabledPlugins(): Promise<InstalledPlugin[]>;
+    /**
+     * Returns whether plugin is recorded as installed.
+     */
+    isPluginInstalled(pluginId: string): Promise<boolean>;
+    /**
+     * Installs marketplace plugin via host adapter and persists state.
+     */
+    installPlugin(plugin: PluginMetadata): Promise<InstalledPlugin>;
+    /**
+     * Removes plugin from host and clears persisted install state.
+     */
+    uninstallPlugin(pluginId: string): Promise<void>;
+    /**
+     * Enables or disables installed plugin.
+     *
+     * Disabling triggers `registry.unregisterPlugin` when registry exists.
+     * Enabling only updates persisted state; host controls actual load timing.
+     */
+    setPluginEnabled(pluginId: string, enabled: boolean): Promise<InstalledPlugin | null>;
+    private readStoredInstalledPlugins;
+    private writeStoredInstalledPlugins;
+}
+//# sourceMappingURL=PluginMarketplaceManager.d.ts.map