feat: the Discord Add panel's artist field autocompletes against FabledCurator's artists (milestone 429)

Operator, after the first live run: "I need the extension to offer an
autofill search function so it's easier to match an entry with an existing
artist."

- The field searches as soon as the panel opens (the server name, usually)
  and on every keystroke; matches list under it, with ↑/↓, Enter/Tab to pick,
  Esc to close, and a last "+ New artist" row.
- Inline autofill: the rest of the top match is filled in and selected, so
  typing on replaces it and Tab/Enter accepts it. Backspacing never refills.
- A result whose name IS the text, spacing and case aside, is picked on its
  own; the hint says in green which existing artist the source will join.
- /api/artists/autocomplete also matches ignoring spacing and punctuation
  ("Tamada Heijun" finds "TamadaHeijun"), ranked just below an exact match.
  The web UI's artist search gets it too.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LVjrnpQjRgHdvq95rASoiR

extension/lib/chip.js

@@ -78,3 +78,30 @@ function discordAddRequest(choice) {
   const name = (choice.artistName || '').trim();
   return name ? { url, artistName: name } : null;
 }
+
+/**
+ * An artist name reduced to what identifies it: lowercase letters and digits
+ * of any script, nothing else — so "Tamada Heijun", "tamada_heijun" and
+ * "TamadaHeijun" are one name. Mirrors the server's autocomplete (#429).
+ */
+function squashName(name) {
+  return String(name || '').toLowerCase().replace(/[^\p{L}\p{N}]/gu, '');
+}
+
+/** The search result that IS the query, spacing aside, else null. */
+function exactArtistMatch(query, results) {
+  const q = squashName(query);
+  if (!q) return null;
+  return (results || []).find((a) => squashName(a.name) === q) || null;
+}
+
+/**
+ * Inline autofill: the first result whose name extends what was typed
+ * (case-insensitive), so the panel can fill in the rest and select it —
+ * typing on overwrites it, Tab or Enter accepts it. null when none does.
+ */
+function inlineCompletion(typed, results) {
+  const t = String(typed || '').toLowerCase();
+  if (!t) return null;
+  return (results || []).find((a) => a.name.length > t.length && a.name.toLowerCase().startsWith(t)) || null;
+}