fix(drone): resolve critical pipeline, frontend, and input validation issues

Data pipeline (critical): scanners/detectors now write to a separate _obs_queue;
a relay thread reads observations and calls correlator.process(), which emits
processed DroneContact dicts to drone_queue for SSE. Without this the SSE stream
received raw unserializable dataclass objects causing JSON errors.

Frontend (critical):
- Add droneContactList container to drone.html so contact cards render
- Add droneMap container and initialize Leaflet in drone.js init()
- Define dsc-distress-pulse keyframes in drone.css (was referenced but missing)
- Fix SSE reconnect: null _sse before setTimeout to prevent _connectSSE no-op loop

Other fixes:
- Validate rtl_sdr_index with validate_device_index(), return 400 on bad input
- Move _ensure_workers() inside _drone_lock to prevent double-initialization race
- Add double-call guard to RemoteIDScanner.start()

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

routes/drone.py

@@ -3,6 +3,7 @@
 from __future__ import annotations
 
 import logging
+import queue
 import threading
 
 from flask import Blueprint, Response, jsonify, request
@@ -13,6 +14,7 @@ from utils.drone.correlator import DroneCorrelator
 from utils.drone.remote_id import RemoteIDScanner
 from utils.drone.rf_detector import RFDetector
 from utils.sse import sse_stream_fanout
+from utils.validation import validate_device_index
 
 logger = logging.getLogger("intercept.drone")
 
@@ -21,18 +23,37 @@ drone_bp = Blueprint("drone", __name__, url_prefix="/drone")
 _correlator: DroneCorrelator | None = None
 _remote_id_scanner: RemoteIDScanner | None = None
 _rf_detector: RFDetector | None = None
+_obs_queue: queue.Queue | None = None  # raw observations from scanners/detectors
+_relay_thread: threading.Thread | None = None
 _drone_running = False
 _drone_lock = threading.Lock()
 
+_SENTINEL = object()
+
+
+def _relay_observations() -> None:
+    """Read raw observations from _obs_queue and feed them into the correlator."""
+    while True:
+        obs = _obs_queue.get()
+        if obs is _SENTINEL:
+            break
+        if _correlator is not None:
+            _correlator.process(obs)
+
 
 def _ensure_workers() -> None:
-    global _correlator, _remote_id_scanner, _rf_detector
+    global _correlator, _remote_id_scanner, _rf_detector, _obs_queue, _relay_thread
+    if _obs_queue is None:
+        _obs_queue = queue.Queue(maxsize=512)
     if _correlator is None:
         _correlator = DroneCorrelator(output_queue=app_module.drone_queue)
     if _remote_id_scanner is None:
-        _remote_id_scanner = RemoteIDScanner(output_queue=app_module.drone_queue)
+        _remote_id_scanner = RemoteIDScanner(output_queue=_obs_queue)
     if _rf_detector is None:
-        _rf_detector = RFDetector(output_queue=app_module.drone_queue)
+        _rf_detector = RFDetector(output_queue=_obs_queue)
+    if _relay_thread is None or not _relay_thread.is_alive():
+        _relay_thread = threading.Thread(target=_relay_observations, daemon=True)
+        _relay_thread.start()
 
 
 @drone_bp.route("/status")
@@ -61,12 +82,16 @@ def contacts():
 @drone_bp.route("/start", methods=["POST"])
 def start():
     global _drone_running
-    _ensure_workers()
-    wifi_iface = request.json.get("wifi_iface") if request.json else None
-    rtl_index = int((request.json or {}).get("rtl_sdr_index", 0))
-    use_hackrf = bool((request.json or {}).get("use_hackrf", True))
+    body = request.json or {}
+    wifi_iface = body.get("wifi_iface") or None
+    try:
+        rtl_index = validate_device_index(body.get("rtl_sdr_index", 0))
+    except ValueError as exc:
+        return jsonify({"error": str(exc)}), 400
+    use_hackrf = bool(body.get("use_hackrf", True))
 
     with _drone_lock:
+        _ensure_workers()
         if not _drone_running:
             if _remote_id_scanner:
                 _remote_id_scanner.start(wifi_iface=wifi_iface)
@@ -86,6 +111,8 @@ def stop():
             _remote_id_scanner.stop()
         if _rf_detector:
             _rf_detector.stop()
+        if _obs_queue is not None:
+            _obs_queue.put_nowait(_SENTINEL)
         _drone_running = False
     logger.info("Drone detection stopped")
     return jsonify({"status": "ok", "running": False})