[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/devices.md

@@ -1,6 +1,6 @@
 # Devices
 
-Here is an overview of devices supported by OpenMQTTGateway:
+For Bluetooth, the maintained list of supported devices is the [Theengs Decoder compatible devices list](https://decoder.theengs.io/devices/devices.html). For the other technologies, the sections below give an overview of what is supported:
 
 ## For radio frequency devices 
 OpenMQTTGateway can support a wide range of 433mhz/315mhz devices, all the ones with SC5262 / SC5272, HX2262 / HX2272, PT2262 / PT2272, EV1527, RT1527, FP1527, HS1527 chipsets are supported by the RF gateway. Added to that RF2 support Kaku and Pilight an [huge list](https://wiki.pilight.org/devices).