fix: address PR #145 review issues

- Escape ac.icao, callsign, typeCode with escapeHtml() in aircraft card (XSS)
- Add linking comments between duplicated IATA_TO_ICAO mappings
- VDL2 sidebar: single-click selects aircraft, double-click opens modal
- Remove stale ICAOs from acarsAircraftIcaos in cleanupOldAircraft()
- Add null guard to drawPolarPlot() in weather-satellite.js
- Move deferred imports (translate_message, get_flight_correlator) to module level
- Check all frequency checkboxes by default on initial load
- Remove extra blank lines and uncertain MC/MCO airline code entry
- Add TODO comments linking duplicated renderAcarsCard implementations

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

templates/partials/modes/acars.html

@@ -111,7 +111,7 @@
         container.querySelectorAll('input:checked').forEach(cb => previouslyChecked.add(cb.value));
 
         container.innerHTML = freqs.map((freq, i) => {
-            const checked = previouslyChecked.size === 0 ? (i === 0 ? 'checked' : '') : (previouslyChecked.has(freq) ? 'checked' : '');
+            const checked = previouslyChecked.size === 0 || previouslyChecked.has(freq) ? 'checked' : '';
             return `
                 <label style="display: flex; align-items: center; gap: 3px; padding: 2px 6px; background: var(--bg-secondary); border-radius: 3px; cursor: pointer;">
                     <input type="checkbox" class="acars-main-freq-cb" value="${freq}" ${checked} style="margin: 0; cursor: pointer;">
@@ -188,6 +188,7 @@
         return `<span style="display:inline-block;padding:1px 5px;border-radius:3px;font-size:8px;font-weight:700;color:#000;background:${color};">${lbl}</span>`;
     }
 
+    // TODO: Similar to renderAcarsCard in templates/adsb_dashboard.html — consider unifying
     function renderAcarsMainCard(data) {
         const flight = escapeHtml(data.flight || 'UNKNOWN');
         const type = data.message_type || 'other';