docs: default and "node" runtime track the current Node.js LTS

Docs now state that an unset `runtime`, or `runtime: "node"`, tracks the
current Node.js LTS (today 24) rather than a pinned version. Explicit
ids like `node-22`, `node-24` and `node-26` still pin to a specific
version.

Mono-RevId: a62eb9fc152bcc12f8ab04cacbb9a9bf542c3028

Author: carderne

docs/config/config-file.mdx

@@ -269,6 +269,8 @@ export default defineConfig({
 
 ## Runtime
 
+If you don't set a `runtime`, your tasks run on the current Node.js LTS. Setting `runtime: "node"` does the same thing — see the Node.js versions section below to pin a specific version instead.
+
 We currently only officially support the `node` runtime, but you can try our experimental `bun` runtime by setting the `runtime` option in your config file:
 
 ```ts trigger.config.ts

docs/manual-setup.mdx

@@ -168,7 +168,7 @@ export default defineConfig({
 
 ### Using the Bun runtime
 
-By default, Trigger.dev will use the Node.js runtime. If you're using Bun, you can specify the runtime:
+By default, Trigger.dev runs your tasks on the current Node.js LTS. If you're using Bun, you can specify the runtime:
 
 ```typescript
 import { defineConfig } from "@trigger.dev/sdk";

docs/snippets/node-versions.mdx

@@ -1,12 +1,12 @@
-Trigger.dev runs your tasks on specific Node.js versions:
+Trigger.dev runs your deployed tasks on one of these runtimes:
 
-- Node.js `21.7.3` (default)
-- Node.js `22.16.0` (`node-22`)
-- Node.js `24.18.0` (`node-24`)
-- Node.js `26.4.0` (`node-26`)
-- Bun `1.3.3` (`bun`)
+- Node.js `node` — the default, tracks the current Node.js LTS (today `24.18.0`)
+- Node.js `node-22` — `22.16.0`
+- Node.js `node-24` — `24.18.0`
+- Node.js `node-26` — `26.4.0`
+- Bun `bun` — `1.3.3`
 
-You can change the runtime by setting the `runtime` field in your `trigger.config.ts` file.
+If you don't set a `runtime`, or you set `runtime: "node"`, your tasks run on the current Node.js LTS. That version moves forward as new LTS releases land, so set an explicit version — for example `runtime: "node-24"` — if you need it to stay fixed.
 
 ```ts
 import { defineConfig } from "@trigger.dev/sdk";