feat(web): alphabet rail always shows #/A-Z/& with disabled empty buckets

Operator: prior rail only emitted buttons for letters with items, so
jumping to a letter required scrolling to that section first — not
useful as a navigation tool. Rail now always renders the full set so
the page reads as a stable A-Z reference regardless of which letters
are present.

- New bucketFor() classifies the first character into '#' (digits),
  'A'-'Z' (letters), or '&' (everything else). Anchor ids switch
  from per-letter to per-bucket: alpha-#, alpha-A, ..., alpha-&.
- ALPHABET + railEntries hardcode the full # / A-Z / & order.
- Buttons for empty buckets render disabled with a low-opacity tint
  + cursor:default so they read as 'no entries here' rather than
  broken jumps. aria-label changes too — 'Jump to A' (enabled) vs
  'C — no entries' (disabled) so screen readers announce state.
- # / & get verbose labels ('numbers'/'symbols') because the bare
  glyph isn't readable.

Tests rewritten — 4 cases: full-rail-with-disabled-buckets,
DOM-order, populated-bucket ids, and a separate fixture confirming
digit-starting items bucket under '#'.

web/src/lib/components/AlphabeticalGrid.svelte

@@ -11,42 +11,53 @@
     item: Snippet<[T]>;
   } = $props();
 
-  // Tag the first item of each letter so the rail can scrollIntoView
-  // it. Continuous flow — no per-letter row breaks — so packed
-  // alphabets don't waste a row for single-item letters.
+  // Bucket the first character into one of three classes so the
+  // rail can show a stable A–Z layout with '#' for digit-starting
+  // entries (2 Mello, 88-Keys, etc.) and '&' for symbol-starting
+  // ones ($uicideboy$, !!!, etc.). Always uppercase letters.
+  function bucketFor(raw: string | undefined | null): string {
+    if (!raw) return '&';
+    const c = raw.charAt(0);
+    if (/[0-9]/.test(c)) return '#';
+    if (/[A-Za-z]/.test(c)) return c.toUpperCase();
+    return '&';
+  }
+
+  // Tag the first item of each bucket so the rail can scrollIntoView
+  // it. Continuous flow — no per-bucket row breaks — so packed
+  // alphabets don't waste a row for single-item buckets.
   const segments = $derived.by(() => {
-    const out: { letter: string | null; item: T }[] = [];
+    const out: { bucket: string | null; item: T }[] = [];
     let last: string | null = null;
     for (const it of items) {
-      const k = (getKey(it) || '').charAt(0).toUpperCase();
-      if (k !== last) {
-        out.push({ letter: k, item: it });
-        last = k;
+      const b = bucketFor(getKey(it));
+      if (b !== last) {
+        out.push({ bucket: b, item: it });
+        last = b;
       } else {
-        out.push({ letter: null, item: it });
+        out.push({ bucket: null, item: it });
       }
     }
     return out;
   });
 
-  // Distinct first-letters in the order they appear (preserves the
-  // upstream sort: 2 → 8 → A → B → … instead of pure alpha order
-  // because the source is already pre-sorted).
-  const letters = $derived.by(() => {
-    const seen: string[] = [];
-    const seenSet = new Set<string>();
-    for (const it of items) {
-      const k = (getKey(it) || '').charAt(0).toUpperCase();
-      if (k && !seenSet.has(k)) {
-        seenSet.add(k);
-        seen.push(k);
-      }
-    }
-    return seen;
+  // Buckets that contain at least one item — used to grey out the
+  // rail buttons for empty letters (they're still present so the
+  // rail always reads as a stable A–Z reference).
+  const populated = $derived.by(() => {
+    const s = new Set<string>();
+    for (const it of items) s.add(bucketFor(getKey(it)));
+    return s;
   });
 
-  function jumpTo(letter: string) {
-    const el = document.getElementById(`alpha-${letter}`);
+  // Full rail: '#' (numbers) → A–Z → '&' (symbols). Always the same
+  // order so muscle memory works regardless of which letters are
+  // present in the current view.
+  const ALPHABET = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('');
+  const railEntries: string[] = ['#', ...ALPHABET, '&'];
+
+  function jumpTo(bucket: string) {
+    const el = document.getElementById(`alpha-${bucket}`);
     el?.scrollIntoView({ behavior: 'smooth', block: 'start' });
   }
 </script>
@@ -54,25 +65,32 @@
 <div class="alpha-layout">
   <div class="alpha-grid">
     {#each segments as seg, i (i)}
-      <div class="cell" id={seg.letter ? `alpha-${seg.letter}` : undefined}>
+      <div class="cell" id={seg.bucket ? `alpha-${seg.bucket}` : undefined}>
         {@render item(seg.item)}
       </div>
     {/each}
   </div>
 
-  {#if letters.length > 1}
-    <!-- Sticky vertical alphabet rail. Stays vertically centered in
-         the viewport via position:sticky + top:50% + translate; the
-         row of letters survives scroll until the grid leaves the
-         viewport. -->
+  {#if items.length > 0}
+    <!-- Sticky vertical alphabet rail. Always shows the full
+         '#' / A–Z / '&' set so the rail reads as a stable
+         reference regardless of which letters are present in the
+         current view; empty buckets render as disabled buttons so
+         the rail layout stays muscle-memory friendly. Stays
+         vertically centered via position:sticky + top:50%. -->
     <nav class="alpha-rail" aria-label="Jump to letter">
-      {#each letters as letter}
+      {#each railEntries as entry}
+        {@const enabled = populated.has(entry)}
         <button
           type="button"
           class="rail-btn"
-          onclick={() => jumpTo(letter)}
-          aria-label={`Jump to ${letter}`}
-        >{letter}</button>
+          class:disabled={!enabled}
+          disabled={!enabled}
+          onclick={() => enabled && jumpTo(entry)}
+          aria-label={enabled
+            ? `Jump to ${entry === '#' ? 'numbers' : entry === '&' ? 'symbols' : entry}`
+            : `${entry === '#' ? 'Numbers' : entry === '&' ? 'Symbols' : entry} — no entries`}
+        >{entry}</button>
       {/each}
     </nav>
   {/if}
@@ -118,10 +136,14 @@
     cursor: pointer;
     border-radius: 9999px;
   }
-  .rail-btn:hover,
-  .rail-btn:focus-visible {
+  .rail-btn:hover:not(.disabled),
+  .rail-btn:focus-visible:not(.disabled) {
     color: var(--fs-parchment);
     background: color-mix(in srgb, var(--fs-accent) 40%, transparent);
     outline: none;
   }
+  .rail-btn.disabled {
+    color: color-mix(in srgb, var(--fs-ash) 50%, transparent);
+    cursor: default;
+  }
 </style>