feat: bootstrap secure cross-platform assistant

Establish the Electron foundation and pluggable agent runtime so desktop workflows can evolve safely across supported platforms.

Co-authored-by: factory-droid[bot] <138933559+factory-droid[bot]@users.noreply.github.com>

src/main/agent/create-runtime.ts

@@ -0,0 +1,29 @@
+import { BigtokenAgentRuntime } from './bigtoken-runtime'
+import { DemoAgentRuntime } from './demo-runtime'
+import { OpenCodeRuntime } from './opencode-runtime'
+import type { AgentRuntime } from './runtime'
+
+export function createAgentRuntime(defaultWorkspace: string): AgentRuntime {
+  const baseUrl = process.env.GOODBUDDY_OPENCODE_URL
+  const embedded = process.env.GOODBUDDY_OPENCODE_EMBEDDED === 'true'
+
+  if (baseUrl || embedded) {
+    return new OpenCodeRuntime({
+      baseUrl,
+      embedded,
+      defaultWorkspace
+    })
+  }
+
+  const bigtokenApiKey = process.env.GOODBUDDY_BIGTOKEN_API_KEY?.trim()
+  if (bigtokenApiKey) {
+    return new BigtokenAgentRuntime({
+      apiKey: bigtokenApiKey,
+      baseUrl:
+        process.env.GOODBUDDY_BIGTOKEN_BASE_URL ?? 'https://bigtoken.ai',
+      model: process.env.GOODBUDDY_BIGTOKEN_MODEL ?? 'sonnet-5'
+    })
+  }
+
+  return new DemoAgentRuntime()
+}