Suggest brand IDs after brand: and place unknown-brand errors on their line

- Completion for brand values in .archify (YAML) and Archify JSON sources,
  from the bundled brand-marks/catalog.json (107 marks); aliases and
  product names match, so "kafka" offers apache-kafka
- brand/unknown diagnostics carry their JSON pointer only at the start of
  the message; use it when subject.path is missing, so the error lands on
  the brand line instead of the top of the file
- Unit tests for catalog loading, value detection and pointer fallback;
  integration checks for completion and diagnostic placement

Closes #5

test/brands.test.ts

@@ -0,0 +1,44 @@
+import assert from 'node:assert/strict';
+import path from 'node:path';
+import { test } from 'node:test';
+import { brandValueAt, loadBrandCatalog } from '../src/brands';
+import { diagnosticPointer } from '../src/jsonPointer';
+
+const root = path.resolve(__dirname, '..', '..');
+const catalogFile = path.join(root, 'vendor', 'archify', 'brand-marks', 'catalog.json');
+
+test('loads the bundled brand catalog', () => {
+  const brands = loadBrandCatalog(catalogFile);
+  assert.ok(brands.length >= 100, `${brands.length} brands`);
+  const postgres = brands.find((brand) => brand.id === 'postgresql');
+  assert.ok(postgres);
+  assert.ok(postgres.aliases.includes('postgres'));
+  assert.ok(brands.every((brand) => brand.id && brand.title));
+});
+
+test('finds a brand value being typed in YAML', () => {
+  assert.deepEqual(brandValueAt('    brand: ', 'yaml'), { typed: '' });
+  assert.deepEqual(brandValueAt('    brand: post', 'yaml'), { typed: 'post' });
+  assert.deepEqual(brandValueAt('  - brand: apache-ka', 'yaml'), { typed: 'apache-ka' });
+  assert.deepEqual(brandValueAt('    brand: "red', 'yaml'), { typed: 'red' });
+  assert.deepEqual(brandValueAt('  - { id: db, brand: post', 'yaml'), { typed: 'post' });
+  assert.equal(brandValueAt('    label: post', 'yaml'), undefined);
+  assert.equal(brandValueAt('    subbrand: post', 'yaml'), undefined);
+  assert.equal(brandValueAt('    brand: postgresql ', 'yaml'), undefined, 'value already finished');
+});
+
+test('finds a brand value being typed in JSON', () => {
+  assert.deepEqual(brandValueAt('      "brand": "', 'json'), { typed: '' });
+  assert.deepEqual(brandValueAt('{ "id": "db", "brand": "post', 'json'), { typed: 'post' });
+  assert.equal(brandValueAt('      "brand": ', 'json'), undefined, 'not inside the string yet');
+  assert.equal(brandValueAt('      "label": "post', 'json'), undefined);
+});
+
+test('diagnostic pointer comes from subject.path, else from a leading pointer in the message', () => {
+  assert.equal(diagnosticPointer({ message: 'x', subject: { path: '/components/0' } }), '/components/0');
+  assert.equal(
+    diagnosticPointer({ message: '/components/0/brand "aws" is not a built-in brand; closest IDs: airtable' }),
+    '/components/0/brand',
+  );
+  assert.equal(diagnosticPointer({ message: 'Label "x" is wider than node' }), undefined);
+});