[DOCS] Overhaul new-user onboarding, home page, and upload flow (#2347)

Getting started:
- New 15-minute Getting Started guide featuring the two most popular
  tracks (BLE on esp32dev-ble, RF on lilygo-rtl_433), with broker setup
  and a verification step
- Sidebar restructured around the new-user journey; upload options
  numbered by ease; Gitpod upload method removed

Home page:
- VitePress hero with clear actions, larger hero image
- How-it-works pipeline diagram shared as a component (responsive via
  container queries), use-case grid, bigger video tiles without the
  image lightbox, refreshed press coverage list, functions pills
- Support section pointing to Theengs Bridge and
  github.com/sponsors/1technophile

Upload flow:
- Decision-oriented upload landing page (journey strip, method cards,
  comparison table)
- Pre-flight checklist and driver troubleshooting on the web installer
- Guided environment picker (bridge + hardware wizard) replacing the
  filter chips, with manifest-verified recommendations
- Post-flash next-steps card linking to the portal and verification

Board images:
- custom_img key in environments.ini and board photos for all
  web-flashable environments (licenses recorded); private prod_env.ini
  environments excluded from boards-info.json

Corrections:
- RF frequency coverage stated as 433/315/868/915MHz
- Removed references to the retired compatible.openmqttgateway.com
  site (BLE list is decoder.theengs.io), the discontinued Theengs
  Plug, and the private sponsor forum


Claude-Session: https://claude.ai/code/session_01TYysQW8tpmt1dWWuzKhTLi

Co-authored-by: Florian <1technophile@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

docs/prerequisites/broker.md

@@ -3,6 +3,11 @@ The broker will act as an intermediary between OpenMQTTGateway and your [control
 
 All the events or commands could pass by the broker.
 
+::: tip Recommended setup
+* **You use Home Assistant**: install the **Mosquitto broker add-on** (Settings → Add-ons → Add-on store), enable the MQTT integration, and create a dedicated user for the gateway. This is the path followed by the [Getting Started guide](../getting-started.md).
+* **You don't**: install [Mosquitto](https://mosquitto.org/) on any always-on machine (Raspberry Pi, NAS, server), it is lightweight, open source and well documented.
+:::
+
 There are many choices of brokers, here are some of the most popular:
 * [Mosquitto](https://mosquitto.org/) (Open source)
 * [Moquette](https://moquette-io.github.io/moquette/) (Open source)