Adds the new claude-fable-5 model (released 2026-06-09) as a selectable
model alongside the existing Claude models:
- ChatService.ResolveModelId: map "fable" and "fable-5" to claude-fable-5
- index.html: fable-5 option in the model dropdown (after opus-4-8)
- ARCHITECTURE.md: model list + resolution table updated
Default stays opus-4-8. The invite-only sibling Mythos 5 is intentionally
not included.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
