Distinguish military planes

[eightonegulf]

Retrieves whether a plane is military or civilian. Uses the DBFlags field to determine this.
Draws the military planes in a orange color so they are easily distinguished.

[Reid-n0rc]

Hardware & testing methodology: ESP32-C3 Super Mini (esp32-c3-devkitm-1, RISC-V, 320KB RAM), 1.28" round GC9A01 240×240 SPI display, USB-C native serial. Built with PlatformIO, espressif32@6.5.0 platform, Arduino core framework-arduinoespressif32@3.20014.231204, -std=gnu++17. Connected to a real WiFi AP with live ADS-B traffic from opendata.adsb.fi. Verified visually on the physical display that military-flagged aircraft render in the distinct color, plus reviewed the merged code path line-by-line during integration since it touched shared drawing code.

Results: two real bugs, fixed locally in my integration build (not yet upstreamed to this PR branch):

1. Wrong array indexed in the beyond-ring-dot color loop, src/ui/radar_display.cpp:

// Before (bug): iterates `dots[]` but indexes `items[]`
for (size_t d = 0; d < dot_count; ++d) {
  const size_t i = items[d].index;
  drawBeyondRingDot(dots[d].x, dots[d].y,
        planes[i].isMilitary ? radar::kColorMilitaryAircraft : radar::kColorAircraft);
}

// After (fix)
for (size_t d = 0; d < dot_count; ++d) {
  const size_t i = dots[d].index;
  drawBeyondRingDot(dots[d].x, dots[d].y,
        planes[i].isMilitary ? radar::kColorMilitaryAircraft : radar::kColorAircraft);
}

items[] and dots[] are populated independently for different subsets of aircraft (in-ring vs. beyond-ring), so this could read the wrong aircraft's military flag or go out of bounds when dot_count > draw_count.

2. dbFlags type check, src/services/adsb_client.cpp:

// Before (bug): dbFlags is an integer bitmask, not a bool
bool isMilitary(const JsonObject& plane) {
  return plane["dbFlags"].is<bool>() && plane["dbFlags"].as<bool>();
}

// After (fix): bit 0 marks military per the ADS-B feed's convention
bool isMilitary(const JsonObject& plane) {
  return plane["dbFlags"].is<int>() && (plane["dbFlags"].as<int>() & 1) != 0;
}

As written, is<bool>() would almost never match a numeric field, so the military check likely never fired.

After both fixes, military-flagged aircraft rendered in the distinct color correctly on hardware. Recommend applying these before merge.