feat: metadata overlay tweaks — location badge, rounded corners, translucent option

- Location gets its own badge in the lower-left corner (separate from
  the main date/time/people/camera badge at the configured position)
- All overlay badges now use rounded corners (radius 4px) via
  fillRoundRect instead of fillRect
- New setting: 'Translucent background?' checkbox in web UI
  When enabled, badge backgrounds use a checkerboard pattern (every
  other pixel black) instead of solid black, creating a 50% opacity
  effect that lets the underlying image show through
- Refactored all badge drawing through a single drawOverlayBadge()
  helper (metadata, sleep indicator, battery indicator)

Co-authored-by: Cursor <cursoragent@cursor.com>

src/settings.h

@@ -59,6 +59,7 @@ struct Settings {
     // Image pipeline
     uint8_t pipeline_mode;  // 0=dynamic, 1=balanced, 2=none
     uint8_t dither_noise;   // 1=blue noise dither smoothing ON, 0=OFF
+    uint8_t meta_translucent; // 1=checkerboard 50% opacity badge bg, 0=solid black
 
     // Device
     uint8_t led_brightness;