Consolidate RPC commands into unified execute_action dispatcher

Replace individual RPC commands (proxy_start, proxy_stop) with a single
execute_action(ActionInvocation) handler. This simplifies the RPC interface
and enables action chaining through events for workflows like duplicate-then-navigate.

crates-proxy/yaak-proxy-lib/src/actions.rs

@@ -0,0 +1,17 @@
+use serde::{Deserialize, Serialize};
+use ts_rs::TS;
+
+#[derive(Debug, Clone, Serialize, Deserialize, TS)]
+#[serde(rename_all = "snake_case")]
+#[ts(export, export_to = "gen_rpc.ts")]
+pub enum GlobalAction {
+    ProxyStart,
+    ProxyStop,
+}
+
+#[derive(Debug, Clone, Serialize, Deserialize, TS)]
+#[serde(tag = "scope", rename_all = "snake_case")]
+#[ts(export, export_to = "gen_rpc.ts")]
+pub enum ActionInvocation {
+    Global { action: GlobalAction },
+}