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/style.css

@@ -827,8 +827,7 @@ input:-webkit-autofill:focus {
 .calibration-preview {
     position: relative;
     width: 100%;
-    max-width: 500px;
-    aspect-ratio: 16 / 10;
+    aspect-ratio: 16 / 9;
     margin: 20px auto;
     background: var(--card-bg);
     border: 2px solid var(--border-color);
@@ -863,6 +862,54 @@ input:-webkit-autofill:focus {
     font-size: 14px;
 }
 
+.preview-screen-total {
+    font-size: 16px;
+    font-weight: 600;
+    opacity: 0.9;
+    transition: color 0.2s;
+}
+
+.preview-screen-total.mismatch {
+    color: #FFC107;
+}
+
+.preview-screen-controls {
+    display: flex;
+    align-items: center;
+    gap: 6px;
+}
+
+.offset-control {
+    display: flex;
+    align-items: center;
+    gap: 3px;
+    padding: 4px 8px;
+    background: rgba(255, 255, 255, 0.15);
+    border: 1px solid rgba(255, 255, 255, 0.3);
+    border-radius: 12px;
+    font-size: 12px;
+    cursor: pointer;
+    user-select: none;
+}
+
+.offset-control input {
+    width: 36px;
+    padding: 0;
+    background: transparent;
+    border: none;
+    color: white;
+    font-size: 12px;
+    text-align: center;
+    outline: none;
+    -moz-appearance: textfield;
+}
+
+.offset-control input::-webkit-outer-spin-button,
+.offset-control input::-webkit-inner-spin-button {
+    -webkit-appearance: none;
+    margin: 0;
+}
+
 .preview-edge {
     position: absolute;
     display: flex;