Streamline calibration modal: inline controls, dynamic aspect ratio, offset fix

- Move total LEDs counter, direction toggle, and offset input into the
  screen area of the calibration preview
- Remove description paragraph, standalone offset form, and total LEDs banner
- Add mismatch warning (yellow + ⚠) when configured LEDs ≠ device count
- Use actual display aspect ratio for calibration preview
- Fix offset not updating tick labels (buildSegments now starts at offset)
- Remove max-width constraint on preview, add padding for breathing room
- Clean up unused i18n keys from both locale files

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

server/src/wled_controller/static/locales/en.json

@@ -90,8 +90,6 @@
   "settings.saved": "Settings saved successfully",
   "settings.failed": "Failed to save settings",
   "calibration.title": "LED Calibration",
-  "calibration.description": "Configure how your LED strip is mapped to screen edges. Click an edge to toggle test mode.",
-  "calibration.preview.screen": "Screen",
   "calibration.preview.click_hint": "Click an edge to toggle test LEDs on/off",
   "calibration.start_position": "Starting Position:",
   "calibration.position.bottom_left": "Bottom Left",
@@ -101,13 +99,10 @@
   "calibration.direction": "Direction:",
   "calibration.direction.clockwise": "Clockwise",
   "calibration.direction.counterclockwise": "Counterclockwise",
-  "calibration.offset": "LED Offset:",
-  "calibration.offset_hint": "LEDs from LED 0 to start corner (along strip)",
   "calibration.leds.top": "Top LEDs:",
   "calibration.leds.right": "Right LEDs:",
   "calibration.leds.bottom": "Bottom LEDs:",
   "calibration.leds.left": "Left LEDs:",
-  "calibration.total": "Total LEDs:",
   "calibration.button.cancel": "Cancel",
   "calibration.button.save": "Save",
   "calibration.saved": "Calibration saved successfully",