Implement comprehensive ICAO country lookup with complete global coverage

- Fix country field marshaling in JSON output to display countries in web frontend
- Replace incomplete ICAO database with comprehensive allocation table from aerotransport.org
- Add all 120+ countries and territories with correct hex address ranges
- Fix aircraft legend label: change "Medium 34000-136000kg" to "Large 34000-136000kg"
- Ensure complete coverage for all allocated ICAO 24-bit addresses worldwide

Fixes:
- 3C64AE now correctly shows Germany 🇩🇪 (range 3C0000-3FFFFF)
- 4ACB58 now correctly shows Sweden 🇸🇪 (range 4A8000-4AFFFF)
- 04008D now correctly shows Ethiopia 🇪🇹 (range 040000-040FFF)

🤖 Generated with [Claude Code](https://claude.ai/code)

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

assets/static/index.html

@@ -113,7 +113,7 @@
                     </div>
                     <div class="legend-item">
                         <span class="legend-icon commercial"></span>
-                        <span>Medium 34000-136000kg</span>
+                        <span>Large 34000-136000kg</span>
                     </div>
                     <div class="legend-item">
                         <span class="legend-icon cargo"></span>