Fix checklist item ordering and add move up/down buttons

The BASE_CHARS in fractional-index.ts had digits after letters
(A-Za-z0-9), but PostgreSQL sorts digits before letters (0-9A-Za-z),
causing items to appear out of order once positions reached the digit
range. Reordered BASE_CHARS to match DB collation.

Also added up/down arrow buttons on checklist items so users can
reorder them within the list.

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

src/lib/components/ChecklistSection.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { api } from '$lib/utils/api.js';
+	import { generatePosition } from '$lib/utils/fractional-index.js';
 
 	type ChecklistItem = { id: string; title: string; completed: boolean; position: string };
 	type Checklist = { id: string; title: string; position: string; items: ChecklistItem[] };
@@ -95,6 +96,41 @@
 			);
 		}
 	}
+
+	async function moveItem(clId: string, itemId: string, direction: 'up' | 'down') {
+		const cl = checklists.find((c) => c.id === clId);
+		if (!cl) return;
+		const idx = cl.items.findIndex((i) => i.id === itemId);
+		if (idx === -1) return;
+		if (direction === 'up' && idx === 0) return;
+		if (direction === 'down' && idx === cl.items.length - 1) return;
+
+		const targetIdx = direction === 'up' ? idx - 1 : idx + 1;
+		const before = direction === 'up'
+			? (targetIdx > 0 ? cl.items[targetIdx - 1].position : null)
+			: cl.items[targetIdx].position;
+		const after = direction === 'up'
+			? cl.items[targetIdx].position
+			: (targetIdx < cl.items.length - 1 ? cl.items[targetIdx + 1].position : null);
+
+		const newPos = generatePosition(before, after);
+
+		const { ok } = await api(`${basePath}/${clId}/items/${itemId}`, {
+			method: 'PATCH',
+			body: JSON.stringify({ position: newPos })
+		});
+		if (ok) {
+			const newItems = [...cl.items];
+			newItems[idx] = { ...newItems[idx], position: newPos };
+			// Re-sort by position
+			newItems.sort((a, b) => a.position.localeCompare(b.position));
+			onupdate(
+				checklists.map((c) =>
+					c.id === clId ? { ...c, items: newItems } : c
+				)
+			);
+		}
+	}
 </script>
 
 <div>
@@ -132,7 +168,7 @@
 
 			<!-- Items -->
 			<div class="space-y-1">
-				{#each cl.items as item}
+				{#each cl.items as item, idx}
 					<div class="flex items-center gap-2 group">
 						{#if canEdit}
 							<input
@@ -153,14 +189,40 @@
 							{item.title}
 						</span>
 						{#if canEdit}
+							<div class="flex items-center gap-0.5 opacity-0 group-hover:opacity-100 transition">
+								<button
+									onclick={() => moveItem(cl.id, item.id, 'up')}
+									disabled={idx === 0}
+									class="text-gray-300 dark:text-gray-600 hover:text-gray-500 dark:hover:text-gray-400 disabled:opacity-30 disabled:cursor-default p-0.5"
+									title="Move up"
+									aria-label="Move item up"
+								>
+									<svg class="w-3.5 h-3.5" viewBox="0 0 20 20" fill="currentColor">
+										<path fill-rule="evenodd" d="M14.707 12.707a1 1 0 01-1.414 0L10 9.414l-3.293 3.293a1 1 0 01-1.414-1.414l4-4a1 1 0 011.414 0l4 4a1 1 0 010 1.414z" clip-rule="evenodd" />
+									</svg>
+								</button>
+								<button
+									onclick={() => moveItem(cl.id, item.id, 'down')}
+									disabled={idx === cl.items.length - 1}
+									class="text-gray-300 dark:text-gray-600 hover:text-gray-500 dark:hover:text-gray-400 disabled:opacity-30 disabled:cursor-default p-0.5"
+									title="Move down"
+									aria-label="Move item down"
+								>
+									<svg class="w-3.5 h-3.5" viewBox="0 0 20 20" fill="currentColor">
+										<path fill-rule="evenodd" d="M5.293 7.293a1 1 0 011.414 0L10 10.586l3.293-3.293a1 1 0 111.414 1.414l-4 4a1 1 0 01-1.414 0l-4-4a1 1 0 010-1.414z" clip-rule="evenodd" />
+									</svg>
+								</button>
 								<button
 									onclick={() => deleteItem(cl.id, item.id)}
-								class="text-gray-300 hover:text-red-500 opacity-0 group-hover:opacity-100 transition"
+									class="text-gray-300 dark:text-gray-600 hover:text-red-500 p-0.5"
+									title="Delete item"
+									aria-label="Delete item"
 								>
 									<svg class="w-3.5 h-3.5" viewBox="0 0 20 20" fill="currentColor">
 										<path fill-rule="evenodd" d="M4.293 4.293a1 1 0 011.414 0L10 8.586l4.293-4.293a1 1 0 111.414 1.414L11.414 10l4.293 4.293a1 1 0 01-1.414 1.414L10 11.414l-4.293 4.293a1 1 0 01-1.414-1.414L8.586 10 4.293 5.707a1 1 0 010-1.414z" clip-rule="evenodd" />
 									</svg>
 								</button>
+							</div>
 						{/if}
 					</div>
 				{/each}

src/lib/utils/fractional-index.ts

@@ -8,8 +8,8 @@
  * https://observablehq.com/@dgreensp/implementing-fractional-indexing
  */
 
-const BASE_CHARS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
-const MIDPOINT = 'N'; // roughly middle of uppercase range
+const BASE_CHARS = '0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz';
+const MIDPOINT = 'V'; // roughly middle of the charset
 
 /**
  * Generate a position string between `before` and `after`.