Add inline calibration canvas with tick labels, direction arrows, and corner improvements

Replace fullscreen pixel preview with a canvas overlay inside the calibration
modal that shows LED index ticks, direction chevrons, and interactive corner
start position buttons. Fix corner hover centering and disable grow animation
for the active corner.

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

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

@@ -112,17 +112,6 @@
   "calibration.button.save": "Save",
   "calibration.saved": "Calibration saved successfully",
   "calibration.failed": "Failed to save calibration",
-  "preview.title": "Pixel Layout Preview",
-  "preview.button": "Preview",
-  "preview.start": "START",
-  "preview.offset_leds": "Offset: {count} LEDs",
-  "preview.direction.cw": "Clockwise",
-  "preview.direction.ccw": "Counterclockwise",
-  "preview.edge.top": "Top",
-  "preview.edge.right": "Right",
-  "preview.edge.bottom": "Bottom",
-  "preview.edge.left": "Left",
-  "preview.no_calibration": "No calibration data. Please calibrate the device first.",
   "server.healthy": "Server online",
   "server.offline": "Server offline",
   "error.unauthorized": "Unauthorized - please login",