feat: hidden flag, description placeholders, drag handle contrast fix

- Unit and Group get hidden?: boolean — filtered server-side before render
- Hidden group also suppresses all its units from the converter
- New resolveDescription() utility in src/lib/description.ts
  supports {id}, {id:label}, {id:plural}, {id:symbol} placeholders
- ConverterCard pre-resolves descriptions and passes result to ConversionResult
- ConversionResult accepts description prop instead of reading unit.description
- Admin forms: Hidden checkbox added for both units and groups
- drag-handle color overridden to --pico-primary-inverse on selected/drag-over rows
  (white in light/dark themes, black on Dan Mode yellow)

src/components/ConversionResult.svelte

@@ -18,6 +18,7 @@
   let {
     value,
     unit,
+    description = '',
     highlighted,
     isInputUnit = false,
     isYolo = false,
@@ -27,6 +28,7 @@
   }: {
     value: Big | null;
     unit: Unit;
+    description?: string;
     highlighted: boolean;
     isInputUnit?: boolean;
     isYolo?: boolean;
@@ -72,7 +74,7 @@
     {/if}
   </span>
   <!-- Line 2: label + symbol -->
-  <span class="result-label" use:tooltip={unit.description ?? ''}>{unit.labelPlural} ({unit.symbol})</span>
+  <span class="result-label" use:tooltip={description}>{unit.labelPlural} ({unit.symbol})</span>
 </div>
 
 <style>

src/components/ConverterCard.svelte

@@ -2,6 +2,7 @@
   import type { Unit, Group, ResultItem } from '$lib/types';
   import type { Big } from 'big.js';
   import { uniformFontSize } from '$lib/actions/uniformFontSize';
+  import { resolveDescription } from '$lib/description';
   import UnitInput from './UnitInput.svelte';
   import UnitDropdown from './UnitDropdown.svelte';
   import ConversionResult from './ConversionResult.svelte';
@@ -33,6 +34,11 @@
     onsetinput: (id: string) => void;
     onctrlclick: (id: string, value: Big) => void;
   } = $props();
+
+  // Pre-resolve all unit descriptions so placeholders are expanded at render time.
+  let resolvedDescriptions = $derived(
+    new Map(units.map((u) => [u.id, resolveDescription(u.description, units, groups)]))
+  );
 </script>
 
 <article>
@@ -51,6 +57,7 @@
           value={item.convertedValue}
           isYolo={item.isYolo}
           unit={item.unit}
+          description={resolvedDescriptions.get(item.unit.id) ?? ''}
           highlighted={item.unit.id === highlightedUnitId}
           isInputUnit={item.unit.id === fromUnitId}
           onclick={() => onhighlight(item.unit.id)}

src/lib/description.ts

@@ -0,0 +1,52 @@
+import type { Unit, Group } from './types';
+
+/**
+ * Resolves placeholder tokens in a description string.
+ *
+ * Supported formats (using the unit/group's ID):
+ *   {id}         → "Label (symbol)"          e.g. "Shit Ton (shttn)"
+ *   {id:label}   → singular label            e.g. "Shit Ton"
+ *   {id:plural}  → plural label              e.g. "Shit Tons"
+ *   {id:symbol}  → symbol                    e.g. "shttn"
+ *   {id:glabel}  → group label               e.g. "Mass"
+ *
+ * Unknown IDs or fields are left as-is.
+ */
+export function resolveDescription(
+  description: string | undefined,
+  units: Unit[],
+  groups: Group[]
+): string {
+  if (!description) return '';
+
+  const unitMap = new Map(units.map((u) => [u.id, u]));
+  const groupMap = new Map(groups.map((g) => [g.id, g]));
+
+  return description.replace(/\{([^}]+)\}/g, (match, token: string) => {
+    const colonIdx = token.indexOf(':');
+    const id = colonIdx === -1 ? token : token.slice(0, colonIdx);
+    const field = colonIdx === -1 ? '' : token.slice(colonIdx + 1);
+
+    const unit = unitMap.get(id);
+    if (unit) {
+      switch (field) {
+        case '':       return `${unit.label} (${unit.symbol})`;
+        case 'label':  return unit.label;
+        case 'plural': return unit.labelPlural;
+        case 'symbol': return unit.symbol;
+        default:       return match; // unknown field — leave as-is
+      }
+    }
+
+    const group = groupMap.get(id);
+    if (group) {
+      switch (field) {
+        case '':       return group.label;
+        case 'label':  return group.label;
+        default:       return match;
+      }
+    }
+
+    return match; // unknown ID — leave as-is
+  });
+}

src/lib/types.ts

@@ -27,6 +27,9 @@ export interface Unit {
 
   /** Optional human-readable description shown as a tooltip in the converter. */
   description?: string;
+
+  /** If true, this unit is excluded from automatic rendering in the converter. */
+  hidden?: boolean;
 }
 
 /** A group of units sharing a base unit and a universal scale factor. */
@@ -39,6 +42,8 @@ export interface Group {
   toUniversal: number;
   /** Display order for units in the converter. Defaults to 'defined'. */
   sortOrder?: 'defined' | 'alpha';
+  /** If true, this group (and all its units) is excluded from automatic rendering. */
+  hidden?: boolean;
 }
 
 /** Full data payload for units and groups. */

src/routes/+page.server.ts

@@ -4,9 +4,12 @@ import type { PageServerLoad } from './$types';
 export const load: PageServerLoad = () => {
   const data = loadData();
   const config = loadConfig();
+
+  const hiddenGroupIds = new Set(data.groups.filter((g) => g.hidden).map((g) => g.id));
+
   return {
-    units: data.units,
-    groups: data.groups,
+    units: data.units.filter((u) => !u.hidden && !hiddenGroupIds.has(u.group ?? '')),
+    groups: data.groups.filter((g) => !g.hidden),
     yoloLabel: config.yoloLabel ?? 'YOLO mode',
     yoloDescription: config.yoloDescription ?? '(cross-group conversions)'
   };

src/routes/admin/+page.svelte

@@ -861,6 +861,10 @@
         Description <small class="muted">(optional — shown as tooltip in converter)</small>
         <textarea bind:value={unitForm.description} placeholder="e.g. A unit based on…" rows="2"></textarea>
       </label>
+      <label class="checkbox-label">
+        <input type="checkbox" bind:checked={unitForm.hidden} />
+        Hidden <small class="muted">— exclude from converter rendering</small>
+      </label>
       <div class="form-actions">
         <button onclick={saveUnit}>{unitFormNew ? 'Create' : 'Save'}</button>
         {#if !unitFormNew}
@@ -906,6 +910,10 @@
           <option value="alpha">Alphabetical</option>
         </select>
       </label>
+      <label class="checkbox-label">
+        <input type="checkbox" bind:checked={groupForm.hidden} />
+        Hidden <small class="muted">— exclude group and all its units from converter rendering</small>
+      </label>
       <div class="form-actions">
         <button onclick={saveGroup}>{groupFormNew ? 'Create' : 'Save'}</button>
         {#if !groupFormNew}
@@ -1219,6 +1227,19 @@
     gap: 0.5rem;
     margin-top: 1rem;
   }
+  .checkbox-label {
+    display: flex;
+    align-items: center;
+    gap: 0.5rem;
+    cursor: pointer;
+    margin-bottom: 0.75rem;
+  }
+  .checkbox-label input[type=checkbox] {
+    flex-shrink: 0;
+    width: 1rem;
+    height: 1rem;
+    margin: 0;
+  }
   .form-msg {
     padding: 0.5rem 0.75rem;
     border-radius: var(--pico-border-radius);
@@ -1289,6 +1310,12 @@
   .drag-handle:active {
     cursor: grabbing;
   }
+  /* When the row has a primary-colored background, muted grey/orange disappears.
+     Force the handle to the primary inverse (white in normal themes, black in Dan). */
+  .tree-unit-row.selected .drag-handle,
+  .tree-unit-row.drag-over-unit .drag-handle {
+    color: var(--pico-primary-inverse);
+  }
   .drag-over-unit {
     border-top: 2px solid var(--pico-primary);
   }