feat(sdr): local receivers — browser RTL-SDR, Local ADS-B layer and decoder feeds (#732)

Adds a Local ADS-B layer fed by your own receivers: a browser WebUSB
RTL-SDR (with FM listening) and local 1090/978 MHz decoder feeds
(LOCAL_RECEIVER_FEEDS, local and private addresses only). Local aircraft
draw in magenta with class, silhouettes, 3D models, trails and a position
sanity filter; the click card names the band and input that heard them.

Builds on Sameh Khamis's SDR prototype and the initial GEV port by
Mazeyar Moeini Feizabadi (#134); the decoder-feed design follows the
notes on #57. Closes #57.

Co-authored-by: Sameh Khamis <[email protected]>
Co-authored-by: Mazeyar Moeini Feizabadi <[email protected]>

.env.example

@@ -129,6 +129,13 @@ AISSTREAM_API_KEY=
 # 0 disables the silence watch entirely.
 # AISSTREAM_SILENCE_TIMEOUT_MS=120000
 
+# Optional: local ADS-B decoder feeds for the Local ADS-B layer. SERVER-SIDE
+# ONLY. Comma-separated band=url entries; band is 1090 or 978 (UAT). Each host
+# must be loopback, a private (RFC1918) address, localhost or a *.local name;
+# the path must end in aircraft.json. Invalid entries are logged and skipped.
+# See docs/LOCAL-RECEIVERS.md.
+# LOCAL_RECEIVER_FEEDS=1090=http://localhost:8080/data/aircraft.json,978=http://localhost:8978/data/aircraft.json
+
 # Optional: TomTom live traffic flow (BYOK freemium — the free tier is 200,000
 # Traffic Flow & Incidents tile requests per MONTH, not per day; no credit card
 # required. Get a key at https://developer.tomtom.com). SERVER-SIDE ONLY: