core: add Bun runtime support for Hono server

Enables running the agent on Bun runtime in addition to Node.js by
abstracting server initialization into runtime-specific adapters. The
server will automatically use Bun's native APIs when available.

packages/opencode/package.json

@@ -39,6 +39,11 @@
       "bun": "./src/pty/pty.bun.ts",
       "node": "./src/pty/pty.node.ts",
       "default": "./src/pty/pty.bun.ts"
+    },
+    "#hono": {
+      "bun": "./src/server/adapter.bun.ts",
+      "node": "./src/server/adapter.node.ts",
+      "default": "./src/server/adapter.bun.ts"
     }
   },
   "devDependencies": {