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.cpp

@@ -24,6 +24,7 @@ Settings SettingsManager::get() {
     s.time_fmt      = readString("time_fmt", "%H:%M:%S");
     s.pipeline_mode  = readU8("pipe_mode", DEFAULT_PIPELINE_MODE);
     s.dither_noise   = readU8("dith_noise", DEFAULT_DITHER_NOISE);
+    s.meta_translucent = readU8("meta_trans", 0);
     s.led_brightness = readU8("led_bright", DEFAULT_LED_BRIGHTNESS);
     s.show_battery  = readU8("show_batt", 1);
     s.queue_cursor  = readU32("queue_cursor", 0);
@@ -45,6 +46,7 @@ void SettingsManager::save(const Settings& s) {
     writeString("time_fmt", s.time_fmt);
     writeU8("pipe_mode", s.pipeline_mode);
     writeU8("dith_noise", s.dither_noise);
+    writeU8("meta_trans", s.meta_translucent);
     writeU8("led_bright", s.led_brightness);
     writeU8("show_batt", s.show_battery);
     writeU32("queue_cursor", s.queue_cursor);