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/jsonPointer.ts

@@ -6,6 +6,14 @@ export interface OffsetRange {
   end: number;
 }
 
+/**
+ * The JSON pointer an Archify diagnostic is about. Most diagnostics carry it
+ * in subject.path; brand diagnostics only start their message with it.
+ */
+export function diagnosticPointer(diagnostic: { message: string; subject?: { path?: string } }): string | undefined {
+  return diagnostic.subject?.path ?? /^(\/[^\s"]+)\s/.exec(diagnostic.message)?.[1];
+}
+
 /** Splits an RFC 6901 JSON pointer into path segments. */
 export function pointerSegments(pointer: string): (string | number)[] {
   if (!pointer || pointer === '/') return [];