feat: online art Generate — configured endpoint, cached into the library
Add the art tray's online Generate: prompt → a GM-configured image-gen
endpoint → new pencil image cached into a persisted, searchable library
(offline thereafter). No endpoint or key is hardcoded — the GM pastes
their gen URL (⚙ field, persisted). Degrades gracefully: unconfigured or
offline → Generate disabled, library search fully works; network is never
load-bearing.
- src/art/generate.js: createArtGenerator (injectable fetch/navigator).
- src/art/library.js: pure addGenerated (dedupe + cap 24).
- art-tray: generate row, endpoint config, generated cache (gmd.art.*).
Tests: generate.test.js, library.test.js, art-tray-generate.test.js;
existing art-tray tests unchanged. 206 tests pass; build clean.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
