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>

docs/en/SUMMARY.md

@@ -1,6 +1,6 @@
 - [Introduction](index.md)
   - [Basic Concepts](getting_started/px4_basic_concepts.md)
-
+- [Try PX4 (Simulation)](simulation/px4_simulation_quickstart.md)
 - [Multicopters](frames_multicopter/index.md)
   - [Features](features_mc/index.md)
     - [Flight Modes](flight_modes_mc/index.md)
@@ -474,6 +474,7 @@
       - [Worlds](sim_gazebo_classic/worlds.md)
       - [Multi-Vehicle Sim](sim_gazebo_classic/multi_vehicle_simulation.md)
     - [Simulate Failsafes](simulation/failsafes.md)
+    - [Pre-built Packages](simulation/px4_sitl_prebuilt_packages.md)
   - [Hardware](hardware/index.md)
     - [Flight Controller Reference Design](hardware/reference_design.md)
     - [Manufacturer’s Board Support Guide](hardware/board_support_guide.md)