v0.8.0: POTUS fleet tracking, full aircraft color-coding, carrier fidelity, UI overhaul

New features:
- POTUS fleet (AF1, AF2, Marine One) with hot-pink icons + gold halo ring
- 9-color aircraft system: military, medical, police, VIP, privacy, dictators
- Sentinel-2 fullscreen overlay with download/copy/open buttons (green themed)
- Carrier homeport deconfliction — distinct pier positions instead of stacking
- Toggle all data layers button (cyan when active, excludes MODIS Terra)
- Version badge + update checker + Discussions shortcut in UI
- Overhauled MapLegend with POTUS fleet, wildfires, infrastructure sections
- Data center map layer with ~700 global DCs from curated dataset

Fixes:
- All Air Force Two ICAO hex codes now correctly identified
- POTUS icon priority over grounded state
- Sentinel-2 no longer overlaps bottom coordinate bar
- Region dossier Nominatim 429 rate-limit retry/backoff
- Docker ENV legacy format warnings resolved
- UI buttons cyan in dark mode, grey in light mode
- Circuit breaker for flaky upstream APIs

Community: @suranyami — parallel multi-arch Docker builds + runtime BACKEND_URL fix (PR #35, #44)

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

Former-commit-id: 7c523df70a2d26f675603166e3513d29230592cd

frontend/src/components/WikiImage.tsx

@@ -14,7 +14,7 @@ const _cache: Record<string, { url: string | null; done: boolean }> = {};
  *   maxH:     Max height class (default "max-h-32")
  *   accent:   Border hover color class (default "hover:border-cyan-500/50")
  */
-export default function WikiImage({ wikiUrl, label, maxH = 'max-h-32', accent = 'hover:border-cyan-500/50' }: {
+export default function WikiImage({ wikiUrl, label, maxH = 'max-h-52', accent = 'hover:border-cyan-500/50' }: {
     wikiUrl: string;
     label?: string;
     maxH?: string;
@@ -56,7 +56,7 @@ export default function WikiImage({ wikiUrl, label, maxH = 'max-h-32', accent =
                     <img
                         src={imgUrl}
                         alt={label || title.replace(/_/g, ' ')}
-                        className={`w-full h-auto ${maxH} object-cover rounded border border-[var(--border-primary)]/50 ${accent} transition-colors`}
+                        className={`w-full h-auto ${maxH} object-contain rounded border border-[var(--border-primary)]/50 ${accent} transition-colors`}
                     />
                 </a>
             )}