Add RTL-SDR mode switcher, DVB-T to Kodi pipeline, FM radio

Mode switcher (rtl_mode_switch.sh) handles exclusive dongle access
between DVB-T, FM, SDR scanner, ADS-B, spectrum, and HackRF modes.
DVB-T pipeline: RTL-SDR -> GNU Radio demod -> MPEG-TS -> HTTP -> Kodi.
Kodi setup script generates M3U playlist for PVR IPTV Simple Client.
Includes dvbt_rx.py and sdr_tv.py from dvbt-rx project.
WebUI updated with mode switcher, channel selector, and Kodi controls.

build.sh

@@ -21,6 +21,7 @@ FILES=(
     system.prop
     system/
     webroot/
+    scripts/
     BUILDING_MODULES.md
 )