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

src/diagnostics.ts

@@ -1,7 +1,7 @@
 import { parse, ParseError } from 'jsonc-parser';
 import * as vscode from 'vscode';
 import { isArchifyFile, readDiagramSource } from './detect';
-import { rangeForPointer, rangeForPointerYaml, yamlSyntaxProblems } from './jsonPointer';
+import { diagnosticPointer, rangeForPointer, rangeForPointerYaml, yamlSyntaxProblems } from './jsonPointer';
 import { ArchifyDiagnostic, isEvidenceError, validate } from './renderer';
 import { evidenceMode, log, runtimeFor } from './runtime';
 
@@ -133,7 +133,8 @@ export class DiagnosticsController implements vscode.Disposable {
       this.collection.set(
         doc.uri,
         result.diagnostics.map((item) => {
-          const offsets = source.format === 'yaml' ? rangeForPointerYaml(text, item.subject?.path) : rangeForPointer(text, item.subject?.path);
+          const pointer = diagnosticPointer(item);
+          const offsets = source.format === 'yaml' ? rangeForPointerYaml(text, pointer) : rangeForPointer(text, pointer);
           const range = new vscode.Range(doc.positionAt(offsets.start), doc.positionAt(offsets.end));
           const fix = item.supportedFixes?.[0];
           const diagnostic = new vscode.Diagnostic(