Add yaak-actions crate for centralized action system

Implements a unified action system that serves as a single source of truth
for all operations in Yaak (Tauri app, CLI, plugins, deep links, MCP server).

Key features:
- ActionExecutor: Combined registry and execution engine with async RwLock
- ActionHandler: Trait-based handlers using async closures
- Context system: RequiredContext and CurrentContext for action availability
- Action groups: Organize related actions
- TypeScript bindings: Auto-generated via ts-rs for frontend use

Design highlights:
- Handlers are closures (no dependencies on other yaak crates)
- Registration requires both metadata and handler (prevents orphan actions)
- Flexible return values via serde_json::Value
- All methods are async using tokio

All 33 tests passing. Ready for integration with yaak-core and yaak-app.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

crates/yaak-actions/bindings/ActionGroupMetadata.ts

@@ -0,0 +1,32 @@
+// This file was generated by [ts-rs](https://github.com/Aleph-Alpha/ts-rs). Do not edit this file manually.
+import type { ActionGroupId } from "./ActionGroupId";
+import type { ActionScope } from "./ActionScope";
+
+/**
+ * Metadata about an action group.
+ */
+export type ActionGroupMetadata = { 
+/**
+ * Unique identifier for this group.
+ */
+id: ActionGroupId, 
+/**
+ * Display name for the group.
+ */
+name: string, 
+/**
+ * Optional description of the group's purpose.
+ */
+description: string | null, 
+/**
+ * Icon to display for the group.
+ */
+icon: string | null, 
+/**
+ * Sort order for displaying groups (lower = earlier).
+ */
+order: number, 
+/**
+ * Optional scope restriction (if set, group only appears in this scope).
+ */
+scope: ActionScope | null, };