drop native number-input spinners app-wide

The spinner arrows clash with the dark glass UI. One base-layer CSS rule removes
them from every type=number input (admin settings, signals filters, data cleanup,
etc.) — values are typed, and type=number still gives the mobile numeric keypad
and validation.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/styles/globals.css

@@ -12,6 +12,19 @@
     font-family: 'Bricolage Grotesque', system-ui, sans-serif;
   }
 
+  /* Number inputs: drop the native spinner arrows app-wide — they don't fit the
+     dark glass UI. Values are typed; type=number still gives the numeric keypad
+     on mobile and browser validation. */
+  input[type='number']::-webkit-outer-spin-button,
+  input[type='number']::-webkit-inner-spin-button {
+    -webkit-appearance: none;
+    margin: 0;
+  }
+  input[type='number'] {
+    -moz-appearance: textfield;
+    appearance: textfield;
+  }
+
   /* Atmosphere: faint graph-paper grid + citron signal glow + film grain */
   #root {
     position: relative;