docs(sim): add Try PX4 quick-start and pre-built packages reference (#26957)

Adds documentation for the SITL containers and .deb packages introduced in #26495. The containers are now live on Docker Hub: [`px4io/px4-sitl:latest`](https://hub.docker.com/r/px4io/px4-sitl) and [`px4io/px4-sitl-gazebo:latest`](https://hub.docker.com/r/px4io/px4-sitl-gazebo).

The main addition is a [Try PX4 Simulation](https://docs.px4.io/main/en/dev_setup/try_px4) page that leads with a single `docker run` command and gets someone flying in under a minute. It lives in Getting Started, right after Recommended Hardware/Setup, so it's one of the first things new users see.

The existing `.deb` package reference has been moved from `packaging/px4_sitl_deb.md` to `simulation/px4_sitl.md` and expanded to cover both containers and `.deb` packages on one page. Sections are ordered by how people use them: what's available, install, configure, connect QGC/MAVSDK, connect ROS 2.

Other changes:
- README now has a "Try PX4" section with the docker one-liner above "Build from Source"
- Landing page (`index.md`) reworked to lead with "Try PX4" before "For Developers"
- Toolchain page (`dev_env.md`) gets a tip redirecting simulation-only users to pre-built packages
- `getting_started.md` and `SUMMARY.md` updated with links to the new pages
- Simulation index tip updated to mention containers alongside `.deb` packages

The SIH container image is published as `px4io/px4-sitl` (renamed from `px4io/px4-sitl-sih`) so the default lightweight option carries the simplest name. The Gazebo image remains `px4io/px4-sitl-gazebo`.

Also upgrades all GitHub Actions in the SITL workflow to Node.js 24 compatible versions (`actions/checkout@v6`, `actions/cache@v5`, `actions/upload-artifact@v7`, `actions/download-artifact@v8`, `docker/setup-buildx-action@v4`, `docker/build-push-action@v7`) to fix the Node.js 20 deprecation warning ahead of the June 2026 deadline.

---------

Signed-off-by: Ramon Roche <mrpollo@gmail.com>
Co-authored-by: Hamish Willee <hamishwillee@gmail.com>

README.md

@@ -70,7 +70,17 @@ PX4 is an open-source autopilot stack for drones and unmanned vehicles. It suppo
 
 <sub>…and many more: helicopters, autogyros, airships, submarines, boats, and other experimental platforms. These frames have basic support but are not part of the regular flight-test program. See the <a href="https://docs.px4.io/main/en/airframes/airframe_reference.html">full airframe reference</a>.</sub>
 
-## Quick Start
+## Try PX4
+
+Run PX4 in simulation with a single command. No build tools, no dependencies beyond Docker:
+
+```bash
+docker run --rm -it -p 14550:14550/udp px4io/px4-sitl:latest
+```
+
+Open [QGroundControl](https://qgroundcontrol.com) and fly. See [PX4 Simulation Quickstart](../dev_setup/px4_simulation_quickstart.md) for more options.
+
+## Build from Source
 
 ```bash
 git clone https://github.com/PX4/PX4-Autopilot.git --recursive