Adds UIStrings autoload that loads display text from a YAML file, replacing hardcoded strings in HUD and interaction prompt. Copy team can now author UI microcopy in client/data/ui-strings.yaml without touching GDScript. Includes 38 strings across 5 categories and 16 gdUnit4 tests for the parser and lookup API. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>