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/test/chip.spec.js

@@ -106,3 +106,38 @@ describe('Discord Add panel', () => {
     expect(discordAddRequest(choice)).toBe(null)
   })
 })
+
+const { squashName, exactArtistMatch, inlineCompletion } = loadLib('chip.js', [
+  'squashName',
+  'exactArtistMatch',
+  'inlineCompletion'
+])
+
+describe('artist matching for the Add panel', () => {
+  const results = [
+    { id: 1, name: 'TamadaHeijun' },
+    { id: 2, name: 'Tamago' },
+    { id: 3, name: 'Sabu Art' }
+  ]
+
+  it('treats spacing, case and punctuation as the same name', () => {
+    expect(squashName('Tamada Heijun')).toBe('tamadaheijun')
+    expect(squashName('sabu_art!')).toBe('sabuart')
+    expect(squashName('玉田 平順')).toBe('玉田平順')
+  })
+
+  it('finds the result that is the query, spacing aside', () => {
+    expect(exactArtistMatch('tamada heijun', results)).toEqual({ id: 1, name: 'TamadaHeijun' })
+    expect(exactArtistMatch('Tama', results)).toBe(null)
+    expect(exactArtistMatch('  ', results)).toBe(null)
+  })
+
+  it('autofills the first name that extends what was typed', () => {
+    expect(inlineCompletion('tamad', results)).toEqual({ id: 1, name: 'TamadaHeijun' })
+    expect(inlineCompletion('Sab', results).name).toBe('Sabu Art')
+    // Nothing to add once the name is complete, or when nothing extends it.
+    expect(inlineCompletion('Sabu Art', results)).toBe(null)
+    expect(inlineCompletion('heijun', results)).toBe(null)
+    expect(inlineCompletion('', results)).toBe(null)
+  })
+})