feat: add Nostr channel plugin and onboarding install defaults

Co-authored-by: joelklabo <joelklabo@users.noreply.github.com>

extensions/nostr/src/runtime.ts

@@ -0,0 +1,14 @@
+import type { PluginRuntime } from "clawdbot/plugin-sdk";
+
+let runtime: PluginRuntime | null = null;
+
+export function setNostrRuntime(next: PluginRuntime): void {
+  runtime = next;
+}
+
+export function getNostrRuntime(): PluginRuntime {
+  if (!runtime) {
+    throw new Error("Nostr runtime not initialized");
+  }
+  return runtime;
+}