Fix APRS crash on large station count and station list overflow

- Fix infinite loop in updateAprsStationList: querySelectorAll returns a
  static NodeList so the while(cards.length > 50) loop never terminated,
  crashing the page. Use live childElementCount instead.
- Fix station list pushing map off-screen by adding overflow:hidden and
  min-height:0 to flex containers so only the station list scrolls.
- Cap backend aprs_stations dict at 500 entries with oldest-eviction to
  prevent unbounded memory growth.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

routes/aprs.py

@@ -21,8 +21,8 @@ from flask import Blueprint, jsonify, request, Response
 import app as app_module
 from utils.logging import sensor_logger as logger
 from utils.validation import validate_device_index, validate_gain, validate_ppm
-from utils.sse import format_sse
-from utils.event_pipeline import process_event
+from utils.sse import format_sse
+from utils.event_pipeline import process_event
 from utils.constants import (
     PROCESS_TERMINATE_TIMEOUT,
     SSE_KEEPALIVE_INTERVAL,
@@ -53,6 +53,7 @@ aprs_packet_count = 0
 aprs_station_count = 0
 aprs_last_packet_time = None
 aprs_stations = {}  # callsign -> station data
+APRS_MAX_STATIONS = 500  # Limit tracked stations to prevent memory growth
 
 # Meter rate limiting
 _last_meter_time = 0.0
@@ -1371,6 +1372,13 @@ def stream_aprs_output(rtl_process: subprocess.Popen, decoder_process: subproces
                         'last_seen': packet.get('timestamp'),
                         'packet_type': packet.get('packet_type'),
                     }
+                    # Evict oldest stations when limit is exceeded
+                    if len(aprs_stations) > APRS_MAX_STATIONS:
+                        oldest = min(
+                            aprs_stations,
+                            key=lambda k: aprs_stations[k].get('last_seen', ''),
+                        )
+                        del aprs_stations[oldest]
 
                 app_module.aprs_queue.put(packet)
 
@@ -1726,13 +1734,13 @@ def stream_aprs() -> Response:
 
         while True:
             try:
-                msg = app_module.aprs_queue.get(timeout=SSE_QUEUE_TIMEOUT)
-                last_keepalive = time.time()
-                try:
-                    process_event('aprs', msg, msg.get('type'))
-                except Exception:
-                    pass
-                yield format_sse(msg)
+                msg = app_module.aprs_queue.get(timeout=SSE_QUEUE_TIMEOUT)
+                last_keepalive = time.time()
+                try:
+                    process_event('aprs', msg, msg.get('type'))
+                except Exception:
+                    pass
+                yield format_sse(msg)
             except queue.Empty:
                 now = time.time()
                 if now - last_keepalive >= SSE_KEEPALIVE_INTERVAL: